What Causes Nausea And Vomiting After Eating?

After a party/BBQ two weeks ago i had a bout of diarrhoea and the next day developed a weird constant nausea after eating that seems to come near the point of vomiting after a yawn. I explained to the doctor the symptoms and he said it was probbaly gastritis. Its been one week, takign nexium and motilium, but it still affects me after eating, usually about 60-90 minutes after, i get the urge to vomit, but it does nto quite occur. Background- Im 39, healthy weight, relatively fit, used to be quite a bad binge drinker but recently (a year) have reduced that activity to a little over the weekly recommended intake for a male. No major pains or aches, but a slight feeling across the diaphragm, under the ribs. Thanks