5 week old crying with every feed?

my 5 week old cries almost everytime she feeds. She has been feeding on Good Start since we brought her home from the hospital. each feed during the day only for about a week and a half now everytime i feed her she starts off eating no problem, then maybe an ounce or 2 in she'll start crying and then suck again until i have to pull the bottle out because shes crying too much. i try to distract her so she can evetually finish the bottle which only works sometimes. she wants to eat but something is upsetting her. she normally eats 3 to 3.5 ounces but ever since this crying thing it is rare except for overnight or early in the morning. what are the reasons she could be crying? what could it be? something i know is she is really gassy also forgot to mention that she is constantly fidgeting when eating stiffening her legs and moving her arms around. but she also moves a lot even when she's not eating but this seems like a little more. i cant tell if shes arching her back because she always moves so much. going to see the pediatrician in a few days but i dont want them to misdiagnose her with acid reflux as i hear it happens a lot. help!