I need help and reassurance..

I am in quit a situation.. My almost 6 weeks old Lo spits many times during the day.. And some times also a projectile vomiting happens may b 3 times a week.. I hold him upright ( 45 degree) after eating for almost an hour... I change his diapers before eating, i only feed him breast milk .. Breast and bottle feeding same results... Once put flat starts spitting, getting fussy, and might vomit the whole thing out.... I burp and give him dimethicone after every meal.. But gases are always getting the worst of him... So he is fussy most of the time... His doctor is not concerned as long as my Lo gain weight... But i am losing it.. Today 4 am i had to change his clothes 4 times in a time space of an hour!.. He has neck rash apparently from all the spilled milk despite cleaning after every spitt...