My son was like this, he was a 33 weeker. It really sounds like the acid reflux. Just the act of sucking on a bottle can cause a vacuum in the throat and make the reflux much worse while trying to eat, poor little things. Keep on the medicine- it can take a little while to really get to full strength.
When you feed her, keep her head and shoulders really elevated, as close to sitting up as you can. Try not to bounce her on your shoulder or press into her soft tummy when you burp her, opt for rapid tapping on her back and smoothing the palm of your hand up her back. Don't lay her flat on her back for at least 20 min after eating, preferably more. You can get a wedge and elevate her shoulders and head when she sleeps so gravity can help her out a little.
Go for it with the gas drops so long as they are not giving her constipation (they are not absorbed into the bloodstream so you can't overdose, only constipate!) and ask your doc when you can start adding a teaspoon of cereal to her milk (be sure to ask first!) We tried Doc. Browns but found that the playtex nursers were the best thing to keep him from being so gassy and uncomfortable after eating.
Over time we just took to keeping him sitting up in our lap most of the time, back to chest and supporting his head by the bony parts of his jaw. The reflux calmed down as he got a few months older and his little system caught up. Good luck, momma, it gets better!