After two weeks I think a Doctor visit is in order, it could have been a stomach bug or some allergy to food.Could you tell me what foods he is mainly fed ?
Sounds like a virus to me. We've been through these with my 2 1/2 year old and some of them can take a very long time to clear. One that pops into mind is rotavirus. Fevers do not necessarily always accompany a virus.
He should see a Dr. Also, make sure he is staying well hydrated. Food is less important then fluids. Juices, pedialight, even milk. Dehydration is always the biggest concern. Is he energetic or listless? That too can tell you alot. If he is listless and weak, then he should be seen right away.
I hope he feels better soon.