Glad to hear that things improved so much, and I hope this is just a little blip in the radar. Hard to tell with teething in the mix. H eats less, but drinks more with teething. He didn't get his first teeth until nearly 8 months. He has always been a big drinker, though. He does wake a bit with teething. It seems los are different in how they react to teething. If it is teething, do meds or gel or tablets help at all? That may be a good idea to help you figure that. But I can understand being cautious about meds.
It does seem odd that all this is coinciding with the change to formula full time. Talk to your pedi and see what he/she thinks. Like I said, we waited too long to go to the gi. If it takes a while to get in to one, you may ask for a referral and tell your dr you would like to err on the side of making an apt (and cancelling if all should clear up with a tooth appearing or it going away).
As for sleep training, it was so much easier to do when lo was feeling well on his adjusted med dose. It would be nice to rule out any thing medical for you, otherwise it could be in vain (making you both crazy). I felt like I was banging my head on the wall. It really was so much easier to reduce my interventions to get him to sleep, as they became less necessary. ;-)