I noticed that your daughter and my daughter are almost the same age - mine was born on 2/13/05. I also have a 4yo, so I'm ahead of you. I can tell you that it is going to get more challenging, for sure.
I'm somewhat introverted myself - I really need time alone during the day, too, to recharge. So I can relate.
If you can hang in there through New Years, make a plan for the new year. I know you are trying to be AP, but you need time to yourself and there is nothing wrong with that, and it's not going to make you less of an AP mother.
It seems that getting your DH to understand/help more might not be a real option. So...
Start thinking NOW about how you are going to get that time to yourself, work on it now, so that you will be prepared when the baby comes.
For example, does your DD have a regular naptime and bedtime each day? I know that some Moms just kind of "go with the flow" on this - but speaking as an introverted Mom, it does WONDERS for my sanity to know that at about a certain time each day, my girls will be napping/sleeping or having Quiet Time.
About Quiet Time - I would start that ASAP with your DD. This has helped me a lot. I didn't do this for a long time with my 4yo, but just recently, like in the past 2 months, I've started a very specific time of day (during my DD#2's nap) when DD#1 has to have Quiet Time. Actually, we call it "Family Quiet Time" and I really emphasize that *everyone* in the family needs some time alone, Mommy too. I think what happens prior to Quiet Time and after Quiet Time is important, too, because it sets it into a routine for the day. For example, at our house DD#2 goes down for a nap about 2pm. Then DD#1 and I play together for a while until 2:30pm. Then it's Family Quiet Time until 3:30pm, when we get back together for "Snack Time". DD#2 wakes up about 4pm.
About bedtime - I used to be all over the map on bedtime. My DD#1 also slept with me until she was one year's old, and I just about was going insane because she nursed all night long. I had to get her into her own bed and room at the age of one. I don't know what you are doing for co-sleeping, but as an introvert, I have to say - it can be really hard to co-sleep when you need your space and rest.
With my DD#2, I had her in a co-sleeper next to my bed until she was 3-4 months, and then I transitioned her to her own room and bed - very gently, of course. But I did do it. It was another part of me being able to recharge - sleeping on my own in my own bed - I don't know how you feel about all this, and I'm really not trying to talk you out of co-sleeping. I'm just sharing my experience.
Any-hoo - We have developed a very consistent bedtime routine with our girls and so we know that pretty much (unless something is really off), they will be in bed and asleep by 7:30-7:45pm. This has been really important to me - to have a couple hours on my own at the end of the day.
I also get up early in the morning, to have a little time. Even 30 minutes to get a shower and have a cup of tea and read the news makes a huge amount of difference in how the day goes.
What about some help other than your DH? You mentioned family - do they live close by? Can you barter some babysitting with that group of AP Moms you mentioned? Or would they just not go for it? Maybe find some other Moms who are not quite so by-the-book AP? It's ok to be a little mixed on the subject, you know!
I love my girls and have co-slept with them, nursed until almost 2yo, spent lots of time with them, but I'll tell you I have no problem having someone care for them while I run errands!
Just trying to stay sane...
Oh, I wanted to add - about going away for a weekend... that may seem like a long time, but how about something small to start with? How about a morning or afternoon for 4 hours? Do that a couple times, then try being gone for a longer time - like an afternoon and evening for about 6 hours - leave the house about 3pm and come back after your DD is asleep. See how it goes. Do that a couple times. Then maybe try an overnight away - find somewhere to go close by for one night - leave about 3pm again, and come back in the morning before noon. Do that a couple times. Get the idea? This is assuming that your DH can handle DD on his own, but come on... he's the Dad, he needs to be a parent, too, KWIM? I think there is too much emphasis on MOM being the "AP parent" and not Dad, too!