My baby is finally sleeping- but I am not

Baby AY was a decent sleeper for the first 3 months or so. He took a few naps a day (although never scheduled) and slept a five hour stretch at night. Then at three-four months, something went haywire. He started waking up every 2-3 hours at night and usually cat napped in the stroller but did not take longer naps anymore.
It was very frustrating not to be able to have a chunk of time to get things done during the day, because I never knew when he would be waking up. Usually it was at the most inopportune times, like when my hands were sticky with challah dough that I was kneading. For a while I chalked it up to teething, but there were no teeth to be found.
He was also extremely sensitive to noise. Not a good thing for a fourth child in a loud family. A door opening, the door bell, the phone...anything would wake him up. It was not a great situation. I kept trying to put him on a schedule but he was totally erratic, waking and going to sleep at totally different times. He also started to fight going to sleep. If I tried to put him down to nap when he was so tired that he was rubbing both his eyes, he would just howl. I was a cranky and tired mommy.
My friend kept telling me it was time to move him out of my bedroom. I agreed but was worried about having to actually get up and go into the next room in the middle of the night. I was not sure how M would take to sharing his room. And I was very nervous what the kids would do to him in the morning when they woke up before me. All out of love...but still.
Last week I put him in the crib in M's room a few nights in the middle of the night. I would nurse him at 11, put him in the room, then wake up at 3 to his crying, and stumble back to my bedroom with him, where he spent the rest of the night. It was not working well.
This week, though, the kids decided they wanted M to "sleep over" in their room. We dragged a mattress into their room and since Saturday night, M has been sleeping with them, leaving the other bedroom open for AY.
And amazingly, he is actually sleeping. This week he has slept an about 6-9 hours straight. 11-5, 9-5, ...whatever it is, I will take it.  When he wakes up around 5 or 6, I will usually bring him into our bedroom to nurse and sleep a few more hours, thereby ensuring that no one wakes him up and/or jumps into his crib.He seems to need a quiet environment for sleep and that is fine with me. The only problem is, I am still not sleeping well. Most nights I have woken up several times to make sure he is not crying. With our air conditioning blasting, I am nervous that I will not hear him. So far that has not been the case, and I know I can get a baby monitor if I am really worried, but my body is so used to sleeping lightly, that I find myself waking up at 3 or 4 or 5  for no reason. Add to that that most nights some other child is waking us up and I am still one tired mommy.
But there is light at the end of the tunnel. I am hoping in the next few days my sleep rhythm will re-regulate itself and I will actually sleep a 6-8 hour stretch. If you could bottle uninterrupted sleep and sell it, that is what I would want for my upcoming birthday.