Why is my 5 mth grandson sick, everytime hes fed?

we thought it would soon stop, but since birth, he will have a bottle, then throw up half of it..EVERYTIME...hes now on solids & does it with this new food too..we tried changing formulas, but this makes no difference..is his stomach under developed?..maybe he has a hyietis hernia..Hes a happy, chubby baby..& gaining weight nicely..& burps very well after each feed...but hes starting to worry me...any sensible ideas or solutions here??