Have consulted my La Leche Breastfeeding Answer Book, I thought I would copy out what it says for you Ames.
It refers to babies being sick as 'spitting up'.
It says
"It is not uncommon for babies to spit up regularly after nursing. Even if the baby is spitting up a lot of milk, he is probably doing fine.If the mother is worried, suggest she keep track of the number of wet diapers and bowel movements her baby has in a 24 hour period. If he has six to eight wet cloth diapers (five to six disposable diapers) and at least two bowel movements (fewrwe bowel movements are considered normal if he is older than six weeks), she can feel confident that her baby is getting enough. Weight gain is another reliable indicator. If he is gaining at least four ounces a week, the mother can be sure that he is getting enough to eat even if he spits up a lot.
Tell the mother that a normal, healthy baby usually outgrows his spitting up within four to six months. Until it clears up on it's own, suggest the mother try gentle handlin and keeping the baby upright after feedings. Limiting nursing to one side per feeding may also help, especially if the mother thinks her baby's spitting up is related to getting too much milk at a feeding.
Some babies spit up because they are getting too much milk too quickly. If the baby gulps or chokes after the mother's let-down occurs, suggest she try taking him off the breast for a minute or two and catching the milk in a towel or diaper, putting the baby back on once the initial flow of milk has passed."
The book does go on to suggest that babies who regularly spit up after feeds should be seen by the doctor to rule out pyloric stenosis, the symptoms of which usually begin when the baby is between two and six weeks of age.
Hopefully something there might help. If feeding uphill doesn't make a difference, you could just try postioning him in such a way so that he is more upright. Have you tried the rugby ball hold, with him back to front. You might find that an easier way of getting him more upright.