I've tried everything, why won't he eat?

my 12month old doesn't eat much, i have tried so many concoctions, baby foods, table food etc.. he takes a few bites and then doesn't want anymore...i have to do all kinds of tricks just to get him to eat a few spoonfuls and i'm exhausted...some days he does eat, but majority of the time it's only a few bites, so far he's in his proper weight cl, although he is smaller than alot of one year olds, the doctor is not complaining also he's on vitamins, but why won't he eat?