HUGE hugs. There's so much new information to process after a diagnoses, and I know that I sure had some feelings of jealousy watching people who had "easy" kids. But honestly, it gets better over time as you and your child learn more about how to manage as yourselves and each other. Even without an initial correct diagnoses (DS is in the autism spectrum, Asperger's would be the closest fit for him, too), all the various evaluations and therapies he had really worked. It's tough getting through them at first (I felt like I needed a day planner on just one kid's life, and one of my other three kids was like that for a good while, too), and things are new and stressful, but then you gain skills to cope.
We had the same issue with stimulant medication and autism symptoms (although at the time they were labeled tic disorder and OCD symptoms). We had some luck with Straterra, which is a non stimulant ADHD medication. He is currently on SSRI's (for anxiety and obsessiveness) and no ADHD meds and is doing the best ever, but he may have been a case of the ADHD diagnoses not fitting, and his autism symptoms are definitely the larger issue. I have heard of off label use of SSRI's for ADHD ((close family friend is a child psychiatrist) but you'd have to discuss this with a very trusted professional to see what you think of that. Straterra's labeled use is an ADHD medication, and more generally accepted. It tends to also slightly reduce anxiety. Try having a talk about your med options with your child's practitioner.
I think it's great you are seeing a psychologist. For me, I mostly dealt with the anger and sadness by practicing yoga, going to church and talking to my minister (yeah, I'm an oddball Christian yogi, but so was my main teacher!), spending time in the garden, and discussing here on mothering and with my friend who also has a son on the spectrum. I didn't feel like my life was as crazy when I had some perspective from other people who had been in the same situation.