SUGGESTION: silent reflux

My daughter was born at 31 weeks last November. She's healthy but she has silent reflux. Scares the living shit out of me when she gags on the built up acid coming back from when she eats. The doctor put her on Zantac. It helps but she still pukes consistently even after many healthy burps. She's constantly swallowing and she's drooling more. We feed her upright we sit her up after every feed for more than 30 mins and has done literally everything the doctor said to do we've even started putting a little cereal in her bottle to thicken up the milk but she's still having these choking spells to where mucus and acid come flying out of her nose and mouth And she panics. She's almost 4 months and It's incredibly stressful. I want her to be happy I don't want her tummy to hurt😢😢😢