Excessive spit up

Help! My 20 week old has always spit up but lately its ALOT. Its like he throws up half the bottle? What am i doing wrong? He eats about 6-7oz every 3-4 hours. Ive tried cutting back on oz but hes a hungry kid and screams until hes fed. Right now hes on Similac Pro-total comfort- should i consider switching formulas?

If i have him up right over my shoulder he spits up so much or even sitting up- its like anytime his stomach has pressure on it? Maybe he has another issue? My doctors office is closed till monday so figured i would ask for advice here until i speak to his pediatrician. TIA