Why isn't my son sleeping anymore?

My 21 month old has always been pretty good about his bedtime routine. He could sleep for 12 hours with no problem, even if he went to bed at like 9:30-10. Then, he started waking up at 8am, no matter what, so we worked with it. Nap time was about 1pm, and bed time became 8:30. Now, me and my boyfriend are to the point of sheer exhaustion. He will go to bed around 8:30, now with much difficulty, and will wake up at about 2-2:30 am. He can now crawl out of the playpen he's been sleeping in, and will get in bed with us. My housing situation is not the best. Me, my boyfriend, and my son all share the smallest room in the house, with my little sister and her daughter in the next biggest room, and my mom in the master. But he crawls out of his bed and into ours, and will act like he's going to go back to sleep, but will get up just about every 20 minutes until about 5am, then he's just up. He sometimes takes naps, but not consistently, like he used too. My mom said me and my sisters never really did this because we had more stability and didn't all stay in the same room... I don't know what to do to help, because him leaving the room isn't even an option, until my mom n sister move out in a month or two... HELP!!!