Going crazy, cannot get this sleep thing down!

As the title states, I feel like I am going insane. Our almost 16 month old foster son is so hot and cold on sleep. Some weeks he'll sleep through every night and I'll think "ok, we finally did it!" and then he'll go through 3-4 nights where he'll be up for 2-3 hours at a time.I just cant fathom what we're doing wrong. About a month ago we transitioned from 2 naps to 1 (usually 11-1) when he started consistently waking at 5:45 or earlier and the transition went more smoothly than I thought it would. However, we're back to being up for HOURS every night. I understand some kids just don't sleep through the night until older, but being up for hours makes me think there's something else going on.Some background: he was placed with us at 6 months and has never been a great sleeper. He's allergic to dairy so we avoid that and will be starting to keep a food diary because I feel like it might be some foods upsetting his stomach and keeping him up. He seems to be constantly teething, but ibuprofen and Tylenol during the night don't seem to do anything to make him more comfortable. When he's up we've tried CIO (going in at 5,10,15 minutes) and he has been sleep trained and goes to bed like a champ but we've done that for up to 2 hours in the middle of the night and he still won't go to sleep. We've also tried rocking him to sleep, but he'll either bolt upright as soon as we put him in his crib or he'll flop in our arms for an hour trying to get comfortable. He's not inconsolable, calms immediately when we pick him up, he just won't sleep.He goes to bed at 7, wakes around 6:15 on nights when he doesn't wake for hours, but when he is up in the night, he'll usually sleep in which tells me he does need those hours of sleep. We've seen a sleep consultant at our local children's hospital and he basically told us we need to get the dude to go to sleep on his own in the middle of the night, but I just can't do hours and hours of CIO, especially with his background in foster care. Any advice? Anyone have a little that is up for hours? via /r/Parenting http://ift.tt/2BmILzJ