H.,
Unfortunately, it's completely normal. My grandson, about the same age, is driving his mother and I crazy with the same issue. This is how I resolved my worry over his getting balanced things to eat..
My biggest success is using oatmeal.. cooked with cinnamon and vanilla. I add a spoonful of peanut butter, which makes it so tasty there's no need for sugar, and sometimes a mashed banana. He's full, it's healthy with complex carbs, protein, and sometimes a fruit. Sometimes I'll add applesauce or a contairer of baby food fruit of choice. It's the one thing he Never says no to.
My other inspiration as far as veggies, sometimes meats (with the meat you can only add a little cause its dry-ish and I think must change the taste noticeably) was to add baby food mixed veggies, sometimes green sometimes orange to the mac & cheese, orange or squash to spaghetti, anyway you get the idea.
He loves these things, we can indulge his favorites or his whim of the day, and we feel better about making sure he's getting what he needs. In between we still wheedle and cajole with the chicken legs (one minute he loves them next minute you'd think we were trying to poison him lol), veggies, all fruits which really isnt so hard on the little sweetaholic, etc.
Lots and lots of luck,
L.