Baby won't eat enough... Don't know what to do

Leslie
My little one is 19weeks/just over 4 months old... She seems to hate eating. She will be obviously hungry at feeding time but after downing 1oz relatively quickly she pulls away from the bottle crying like it bit her... Then the rest of the feed is a struggle. She wants the bottle but then doesn't... I can't figure out what to do.. We've tried gas drops/gripe water and tons of burping if it's gas and sometimes it seems to be... But it never gives.... We've already got cereal in her bottles to try to get her the calories she's not consuming enough of (doctor recommended) so I would think that would help if it were reflux. She was born exactly four weeks early due to eclampsia so she was/is a preemie so is a little behind because of that. She's not increasing her feeds either... She's only eaten over 4 Oz twice in her lifetime and sometimes were lucky to get her to eat 2 Oz.... I feel like the more we battle her to eat the more she's going to hate it because it's not a pleasant experience cause she cries thru the whole thing.... Other than that she is an extremely happy baby... She's underweight for a four month old but is okay for a 3 month old (her adjusted age)... Any mom's out there with similar problems?? Any advice? I pumped breastmilk until she was 2 months but was always supplementing due to not produce enough milk... She's been on neosure... Didn't do too well... Then was on enfamil gentlease for a while.. It had its good and bad days and just started alimentum... Nothing is improving... Any info on soy and how to know if your child needs it? Help!