Advice needed!! Baby whines while bottle feeding


Hi ladies!

I really need some advice, lately my 4 month old will whine/ cry whenever she eats. She’s been doing this for over a week now and I can’t seem to figure out why..She’s bottle fed and on a size 2 nipple (dr brown bottles) she’s always done really well with those bottles, so I don’t think that’s the issue.. she was diagnosed with GERD when she was 7 weeks old and has been on generic Prevacid 7.5 mg 1 a day since about 10-11 weeks (Zantac didn’t work for her) 2 1/2 weeks ago she seemed to be bothered by her GERD again so doc said it was ok to bump her up for a full dissolvable tablet (15mg) cut in half, once in the morning and at night. I was reading the side effects online about the medication and it said it can cause stomach pains and a list of all sorts of side effects.. but if she’s been on it for so long why all of a sudden??? On top of that, 2 of her top teeth are starting to come thru.. I’m at my wits end trying to figure out why she’s in pain, and as a mommy it’s hard to watch. Just this last feeding she was whining really bad and once she did finish her bottle she was VERY squirmy, would not stay still and hunching over like her stomach hurt.. do you think ALL of these issues combined could be the cause? Or does one seem to be more prevalent than the others?? Or am I totally off on her behaviors?? When she’s not eating she’s generally happy go lucky! Any suggestions would be greatly appreciated!! (Currently she’s drinking nutramigen, 5.5 oz every 3-4 hours)