19 week old refusing to feed

[SquedgieBeckenheim]

DD2 is 19 weeks old, mix fed (formula through a naso-gastric tube at night) struggles to gain weight due to heart problem. Today she is refusing point blank to feed unless I manage o latch her on when she's half asleep. I don't think shes had much at all today, and we cannot afford to miss any feeds really. She's just screaming, won't even try to latch on.
I'm at my wits end and don't know what to do! She's normally a happy girl and feeds really well.

Has she got any soreness in her mouth? Maybe have a look and see if you have any teeth about to come through?

Could you try a dose of ibruprofen and see if that helps?

Other than that, if she's still cranky I'd call the hospital.

Mine refused around the same time. Nothing I could do - in public, in quiet, in dark, in light etc. I just used to pop on when asleep like you're doing. Rock to sleep for naps and then pop on. Feed throughout the night.
Because prior to this he'd been feeding hourly I was very worried that 3hrly feeds (roughly awake for 2 hours at that age, rock to sleep feed and then asleep for an hour.. sometimes more) wouldn't be enough but actually I think the spaced out feeds were really efficient and he would properly drain the breast which he wasn't doing when he fed more often. He maintained his centile through the nursing strike. It did come back, it almost always does.

Could there be a mild lactose intolerance which causes problems? DS1 refused to breast feed at 12 weeks after the first time he was offered a bottle, because the formula had colief in it which has an enzyme to process the lactose, and so didn't hurt him.

He grew out of it several months later.

thanks for the replies. She's just been weighed and gaining weight fine, so obviously she knows what she's doing and getting enough somehow! She's feeding a bit better, but still fussy at times.
talkin she does have cows milk protein allergy, so I am dairy free.