Foremilk/hindmilk imbalance

I am a FTM and my baby was born 3 weeks early. She is now almost 7 weeks and I have been breastfeeding/pumping since she was born. After about 2 weeks, she dropped weight so I switched to just pumping and giving her my milk through a bottle. I’ve been back to BF and pumping for about 3 weeks now and she is gaining weight BUT has been extremely fussy after feedings, tends to pull off and gasp for air, coughs after feedings, has been spitting up after burping and now actually throwing up, she is VERY gassy and tends to try to pass her bowls but cant do it. I have been using a qtip to relieve her her and ive noticed it is very frothy and bubbly. It’s yellow and still a little seedy but when it comes out it shoots out and then is bubbly. After this she seems better, but then I feed her and it starts all over again.

Im wondering if it’s an imbalance, or a milk allergy. Any thoughts? Recommendations?