For the past week my 5 week old DS has become fussy while drinking his bottle. It's not during every bottle, but when it happens he sucks a few times and all of a sudden his face screws up and he starts crying. It can take an hour for him to finish his bottle as he constantly stops eating, cries in what I assume is pain and then starts crying louder because he's still hungry. He occasionally has little spit ups but not a huge amount and not all the time. He does this for maybe 2 or so bottles per day but it seems to be happening more often - 3-4 times today it seemed. I feed him with his body upright and that seems to help for a little bit but then after a few mins it starts all over again. We burp him frequently during feeds and he does a few burps so i don't think it's wind. We thought maybe reflux but he's really calm and content the rest of the day, it's just during some of his bottles. Is painful reflux more common while they're actually eating rather than at other times? I guess it could be gas but would painful gas only happen while eating? I we use Nan Ha formula.
Any ideas? It's heartbreaking to see him in pain .
Eta - Apologies for my shocking spelling/punctuation, I'm typing one handed.