Dear T.,
Talk to the doctor or nurse when you take him for his regular check ups. Also, when you give him something new, then just give a little to him and watch to see if he is allergic to it. If it makes him breath funny, or throw up, or break out in a rash. If they are going to be allergic, then the reaction may not show up right away. It seems like you are one lucky mama. It is really hard to have a picky eater.
He will slow down at some point and almost stop eating, but just don't fuss at him, if his body needs it, he will eat. Please do not make meal time a time to force anything. It doesn't hurt to ask if he is going to eat something after he has had a chance to taste or eat it, then respect his nod or head shake or no! Take it away,without comment, and offer something else, if you can easily do that. This is not spoiling, and tell the first person who tells you that I said so!. (not a sweet)
Also, during those times when he doesn't eat so well, give him a snack inbetween meals if he asks or wants it. That is not spoiling either, just be sure that it isn't a sweet. Give him something healthful, fruit, raisins, dried fruit, a healthy home made cookie so you can control the amount of sugar, a lot of times I put in 2/3 or 1/2 of the called for sugar and no one ever knows. Or .... you know what to do.
Remember, their tummies are as large as a small fist. Something like that, anyway. Quite small. Have fun, C. N.