i would lean towards reflux, or a weak flap ( cant think of teh technical or anatomically correct name) that sits between the stomach adn the eosophegous.
my brother had this as would basically throw up every time you layed him down or piut him in the car.

see your GP about it or your pead if your refferal is still valid which is should be since he is only 7 montsh old and they are valid for 12 months. and most babies get a blanket referal at birth.