Horrible projectile vomiting =(?

my son will be three month old on the fifth.. ever since a couple of weeks ago he keeps spitting up his formula and its not a lil its a lot like projectile vomiting. i've tried different type cause the doc though tit was the formula but it wasn;t and the doc says he is fine if it isn't the formla i only feed him a 1.5 ounces then burp him then feed him a lil bit more then cut him off at 4 oz, the er doc says its normal and nothing is wrong with him because his weight is fine but i am afraid he will start to lose his nutreints and possibly have this issue get worse. Do any of you have any suggestions? i was told to give him pedialite after a lot of throw up to give him a lil of what he needs instead of losing it all, and she uses it on her son who is the exact same age my son and he is healthy, but docs say its not good for him. what do you think?