The first time Charlie did this i didn't know what was happening, but he hadn't had any during the day so I fed at night. it lasted a few days & i tried my hardest to get him to feed during the day....then all of a sudden 2 teeth popped through. This was around 5.5months....so your bubs could be teething. At the same time he got a snotty sounding nose, woke regularly at night, & red cheeks. I now know the signs, so perhaps it could be that. It hurts so they are often off their food, but go looking for it at night. If bubs hasn't had much during the day I prob would give what's needed at night or you could just get more frequent wake ups. If it's getting used to new formula then it will settle & bubs will get himself back on track. If its something like teeting some get etc during the day to ease pain that might help with feeding more & something at night might create less wake ups. HTH.