Why can't i get more than 4oz in my baby?

He's 14 weeks now and every time we give him more than a 4oz bottle he's violently sick, doc's said reflux and prescribed gaviscon but we've not seen a difference, went back and told nothing wrong with him. anyone else ever come across this..? health visitor suggested we may have to wean early as i'm having to feed him 5 times between 7pm and 7am, after midnight wakes every 2 hours, so hungry more little man