It's time to get tough! Have you thought about putting him in a toddler bed or a twin "big boy" bed?? I'm 32 weeks pregnant with an almost 25 month old daughter. We transitioned her into her "big girl" bed 2 months ago. It was a little tough at first, but she's doing really well in her new bed now & sleeping thru the night. I would suggest putting a safety thing on the door or a baby gate so they cannot run around at night. At first, she would climb out of bed & go to the door crying. I would go in & lead her right back to bed, then stand right by the doorway (but out of her sight). She would climb back down & head for the door, but then when she saw me, she would head back to bed. I was always pretty firm & consistant saying "back in bed, it's na-night time." Now, she pretty much stays in bed...if she drops something she will climb out on her own, pick it up, and bring it back into bed with her. For a while she would wake up once in the middle of the night...I'd go in, make her lay back down & cover her up and say "it's na-night time, I love you." Sometimes she'd cry for a bit, but then she'd fall back to sleep. It took a few weeks but I was just very consistant & now she does very well.
Also, you might want to check to see if your son is cutting his 2-year molars. My daughter went thru a very fussy night time phase when she was cutting her molars....she already has all 4 of hers!!!!
I know it is hard, b/c we've all been thru it....it's late...you're tired....the easiest solution is to hold them & rock them to sleep. But the more you do it, the more they want it....and the less sleep the both of you will get!
Hope this helps some....good luck!