Best formula for acid reflux?

My son was diagnosed with severe acid reflux. He is 4 weeks old. They put him on zantac. It causes him to stop breathing and his oxygen levels to drop. He projectile vomits and is extremly fussy. On top of this they say he is colic. He started out on similac advance and we are now trying similac sensitive. It dosent seem to be making much of a change. I was wondering if anyone else experienced this and what formula worked best for you.