seriously what is going on!

my little man will be 6mo on Monday.  We recently switched him from breastmilk to formula due to me going back full time and not being able to supply his demand. He then started being super fussy all the time and waking up in the middle of the night screaming (when he usually has been STTN for a good 1.5 months) called the pedi and they told us to switch to gentle ease formula, which we did.  That seemed to work as he was again a happy baby and went back to STTN.  Just the past few days all seems well during the day but he is again waking up in the middle of the night.  He would go to sleep and wake up 30-60 min after I put him down. He wouldnt stay sleeping any longer than 30 min in his crib. I was absolutely exhausted and he ended up sleeping in bed with me the past 2 nights =(   He has a runny nose, he's seems to be a little more gassy than normal, and he drools all the time.  I don't know if he is teething, has a cold, has a tummy ache ... I just don't know why he isnt sleeping at night anymore???