Silent reflux and gas -- switching formulas?

My combo fed (90% formula) ex-preemie baby did amazing in the hospital with Similac special care 24, upon discharge was switched to neosure22, started having terrible acid reflux and gas that was worsening over a week, switched to Similac Total comfort per dietician with essentially no difference. It's been a month and she's been suffering from reflux to the point where she has flares every few days that cause hoarseness and stridor, even on pepcid. Gas improved. She's on lovebug probiotics. We tried thickening feeds with gel mix but then really bad constipation occurred so we stopped. Finally, we decided to try transitioning to Bobbie Gentle, first two days went well but then on day 3 she was incredibly painfully gassy leading to really bad reflux. Has this happened to anyone else? Recommendations? What do we doooo