My two yr old son is normally a great eater now lately for the past couple days he is not when do i worry?

Picky Toddler is OK: According to American Academy of Pediatrics it gets 15 tries on average for a toddler to eat a new food,keep trying and don't get discouraged:) provide variety of healthy and new foods every day, if he is acting otherwise ok then that's not an issue. It is very normal for a 2 year old to do so, careful not get into a power struggle over food being 2 is "all about me" !

Come and go: The appetite of the two year old will come and go. He may eat "well" for a few days, then you may have days that you actually wonder if anything got into his mouth! Also keep in mind that from 2 to 3 kids gain far less weight than in the first several years of life. You can check his growth by plotting it here: http://www.cdc.gov/growthcharts/data/set1clinical/cj41c021.pdf