acid reflux in infant

Does anyone have any advice for dealing with acid reflux with their baby? I have tried 4 different formulas, now on similac alimentum, but all seem to produce the same result. He is gaining weight (13 lbs and 3 1/2 months) but the spitting up is terrible! Sometimes it seems like his whole bottle was wasted. I talked to my pediatrician about medication but would rather use that as a "last resort". I have tried spit up formluas and always keep him propped up after feeding for 45 min. Any thoughts on cereal for thickening? Gerber sooth probiotics?