GERD help

my baby is 10 weeks old. he’s been on nutramigen formula for a while to eliminate any cow protein allergy & we’ve been adding rice to bottles (pediatrician reccomended) but he was still spitting up bad. pyloric stenosis was ruled out bc he is gaining weight. so doc said to make his bottles with rice as thick as oatmeal like super super thick. i tried for 2 days & for 2 days he hollered so much. so i’ve been doing just 1 tsp per ounce the past 2 weeks. still spitting up so much. i have no idea what else to do. he’s already been on prevacid & zantac & i’ve tried sitting him up after feeding & during & nothing is helping. any one else been through this or have any advice ?