H.,
I feel your pain! Our son went through almost exactly the same thing last year and all I can remember is how exhausted I was trying to deal with it! Here's what we did and what worked for us(we came up with this plan after a few sleepless nights on my part and a very long discussion): We made sure that we had a very calming, consistent bedtime and bedtime routine, we would both tell him goodnight, then we would walk out of the room and sit down in the hallway out of his sight but close to his room. Then every single time he would get up one of us would get up and put him back in bed without saying a word. Th first night wasn't too bad, I think he only got up twice, but the next two nights he got up a few more times. After the third night though he went straight to sleep and hasn't had a problem with staying in his bed since (he is 3 now)! My husband and I sat out for a few more nights just to make sure he didn't try anything. So a few things that I think made this work for us 1) We were very consistant, no looking back once we started. 2) We did it together, I don't know if your schedule allows this but I really think that this problem is just so exhausting to deal with by yourself, at least it was for me! I also think it helped that my son knew that we were both serious about him staying in bed. It also gave my husband and I a chance to connect a little (while we were waiting for him to fall asleep we watched LOST episodes online, with the sound turned down. It was actully kinda fun and we were a little sad to give it up!) If your husband isn't available to help, I would suggest at least calling a friend or family member to spend a few nights and help out, if at all possible!
Also, naptimes are still kind of a struggle with my son (he doesn't always fall asleep) but because we did this I can put him down for his nap and he will stay in his bed until I come to get him even if he doesn't go to sleep. (We told him he had to stay in his bed until Mom or Dad came to get him)I would suggest setting up something similar so that you (and your son) can get a break.
I hope this helps a little and hang in there!
C.