Hang in there!
I just finished reading this thread, and what a year you've had, mama! I was so happy to see that things have gotten better and so many people have given you such great information.
Like several others, some of your son's behavior reminds me of my oldest ds, who just turned 7. He was a very intense, high-need baby, who I wore or held most of the time and co-slept with. When he became a toddler he was into *everything* -- I quickly learned to baby-safe my house for my own sanity, including putting a latch on the front screen door because my ds thought it was great fun to push it open and run outside. He was (and still is) big for his age, which made those times when he got too too rough or wild harder to deal with, not least of all because other people expected better behavior from a child who *looked* 3 or 4 but was really only 2. Between about ages 3 and 5 I often felt like "that mom" at the park and playgroups; that was the most frustrating period. He wasn't constantly obnoxious, but he was a bundle of energy, constantly moving from one thing to the next and unable to sit still long enough to finish a meal. It really took all of my energy, focus and patience to keep him on an even keel and not lose my temper (although of course sometimes I did.) I sometimes had to carry him to the car kicking and screaming; he became easily overwhelmed with frustration and no amount of patience or understanding helped much at those times. It was my experience too that he was at his worst around me. My mom told me what many others have said, that he felt safe letting loose around me.
By the time he was 4 I had decided to homeschool him. I was certain he would be diagnosed with ADD or ADHD (at least) and was very opposed to medicating him. I ultimately decided it wasn't of much value to me to know that Dr. X thought he had Disorder Y and chose not to have him evaluated. I decided that if his behavior made homeschooling impossible or began to interfere with our everyday lives to an unacceptable extent, I would revisit the decision, and I still feel it was the right one.
One thing that really helped me, of which I was reminded again by moms who mentioned SPD, was reading "Raising Your Spirited Child" by Mary Sheedy Kurcinka. I thought it might be a bit of a warm-and-fuzzy approach because it focuses on avoiding triggers -- just like for children who need lots of physical contact, or become quickly overwhelmed in crowds; in fact these are some of the examples -- and understanding how to notice warning signs. It also helps you (the parent) figure out your own level of "spiritedness" and discusses how that might help or hinder your relationship with your child. Some of the characteristics of spiritedness include energy, intensity, and sensitivity. The book includes a really helpful section on introverts vs. extroverts and how they have different needs. For example, I learned that while I'm an introvert (meaning I need time to myself to recharge my batteries), my ds is an extrovert (meaning he needs to be around other people to recharge his batteries). Either personality type can learn to increase their comfort level in situations that make them uncomfortable (i.e., an introvert participating more in school or an extrovert playing quietly in his room) *but* they really need to be able to spend some time in their comfort zone every day in order to feel good. Realizing this made a huge difference, because I now recognize the need for myself to have alone time, or my ds to play with others.
Time outs usually did not work with him, because I had to sit there next to him and make sure he stayed. I quickly decided it wasn't worth the trouble most of the time and instead focused my energy on having him "atone" -- if he hurt someone, he needed to make them feel better; if he made a mess, he needed to help clean it up.
I am certainly not saying that this book solved all my problems; however it was reassuring to realize there were other kids who had a meltdown if their favorite shirt was in the laundry, or refused a bedtime story if the one he wanted to hear was unavailable. Most importantly, it helped me understand that *I am not responsible for his reactions*. I used to take it very personally when he got upset, and really wanted him to be happy all the time. It seems in retrospect that this often made him more negative, and when I learned to avoid trigger situations and work *with* his spiritedness rather than trying to *make* him do things, we got along a lot better and he was a lot more pleasant to live with. It made the tantrums easier to deal with because they became a lot less frequent.
He still has tons of energy, and daily physical activity is an absolute must for him. Especially when he has been sitting for awhile, when he gets up he is like a whirlwind. He walks back and forth while telling me things, sometimes seeming like he is acting out his story. He is constantly touching things to explore them, running his hands along the wall, drumming on the table, tapping his toes. At mealtimes he sits, then stands, then sits, then leans back in his chair, then puts his legs and bottom off to one side of the chair, then the other, and so on until he's done eating. When he was still doing this at age 4 my dh was worried and thought this was very weird, that we shouldn't allow it (ha-ha!). I was unwilling to spend mealtimes fighting with ds and refused to try to *make* him sit, preferring to focus instead on the "biggies." He still does this, and the only rule I made is that he has to take bites over his plate and clean up any mess he makes. It's working pretty well, and I think everyone feels better just accepting the way he is and not letting his need for movement -- which really is a small thing, in the scheme of things -- bother us or disturb our mealtimes.
Ds has become a kind, loving child who occasionally still has his moments -- don't we all? Things have really gotten better as he's gotten older. I know I am more relaxed in general because I have been a mother for awhile. Again, looking back, I realize that during the most difficult times I was working part-time, and while I'm certainly not passing judgement on employed mothers, it's been much easier to deal with my LOs since I started staying home full-time. It's been my experience that children really need clear expectations and consistent consequences, and of course that's easiest when you're with them most of the time. When you have to work, you have to work, though, and I think that makes it even more important to be consistent in the limited time you have together. I don't necessarily mean punishment, because I think it's very easy to become overly punitive in all of one's dealings with a child and want to punish over every little thing. However, natural consequences are a great teacher, such as getting scratched or bitten by a cat after they wouldn't stop pestering it, or having their favorite shirt not get washed because it was left on the floor instead of being put in the hamper. There are probably lots of better examples...
I had another thought: might your ds enjoy helping you make dinner and do whatever other chores you need to do in the evening? My kids always act up when they need attention. Sometimes just including them in what I'm doing is enough to defuse the situation.
Anyway good luck! I wrote a much longer message than I intended but hopefully there is something useful for you. I hope everything keeps getting better!

Follow Mothering