My 4yr old seems to have a sense of smell like no other, he actually vomits when im cookind and will only eat very few things, is somethn wrong?

Probably not....: As long he is growing and acting normally. Check with your pediatrician to see his growth chart.

Probably not: But one of the medical conditions in which this a symptom is addison's disease (adrenocortical deficiency state). You should allow your pediatrician to examine him. There are, however, many people with an enhanced sense of olfactory perception who are otherwise perfectly normal. Good luck.