hmmm, I am sorry I don't have more input to give
. I had the same problem last week, but, looking for an easy way out, I just kep feeding him to sleep. Turned out he had gas and I was making it worse. After a night of dh helping me get him to sleep w/o feeds, he now only wakes once or twice a night. If it was gas or something like that, I don't think you would be having such an easy time getting him back down.
Are there any noises in the house that might be waking him up (maybe something you wouldn't normally think of like the AC starting???). Maybe turning on some white noise would help. Kind of grasping at straws.
I have to agree with Lana in that sometimes there just isn't a reason. Hopefully one night in the near future you will go to bed and the problem will disappear