I need some tips/ideas on how to handle 1 yr old waking up in the night?

I have no idea why, but for the past 3 nights my 1 year old has been waking up in the middle of the night crying. I try to just leave him be for a bit just to make sure that he's not going to just roll over and go back to sleep, but thats not been the case and so to keep him from crying and waking our 3 year whom he shares a room with I have been having to get up and get him.. I change his diaper, and have been feeding a half of a bottle of milk to try to get him to go back to sleep. I rock, and rock, and rock, and yet this kid will not go back to sleep!! early this morning around 12:30 he did this, I did all of the things I just said, and we sat in this rocking chair rocking until almost 4 in the morning before he actually went to sleep, and stayed asleep when I laid him back in his crib.I just don't get it, he hasn't woken like this at night since he was really small, but even then a bottle feeding and a change was all it took to get him right back down. Nothing has really changed, he eats wonderful all day long, he plays hard with his big brother and with me all day, his room is comfy, not too hot, nice and dark with only a dim night light, and yet getting him to go back to sleep in a decent time frame is near impossible right now.. I guess he could be cutting a tooth, but this morning I even used some orajel and gave tylenol to him and that didn't help either. While sitting here rocking he wants to sit up and talk to me, and tries to play with my hair and stuff. If he were in pain he would be crying and fussy, but the only time he is fussy is when I try to lay him back down before he is fully asleep. I am at a loss, and completely exhausted because then my 3 year old is ready to wake up and start the day before 6:30.... Do any of you have some good ideas how to get this little guy to go back down to sleep at night when he wakes? Like I said, he shares a room with his brother so letting him cry it out is not an option...I will take any advice that I can get!! And if you have no advice, but know how to pray, prayer will work also.lol... We really need to get some good sleep tonight..=)