L.E.
My son is the same way .....very very picky eater since 15 months. He had 105 fever and rushed to emergency room since that day he came home a different baby as in eating. Before he would eat anything I put infront of him and after that incident, most pickest eater ever. I'm so jealous that your son eating chicken...LOL. That's awesome some sort of protein. If I can only wish. My son will not eat any meats, vegs, peanut butter, etc and same thing will not even try alot of things. It's to the point that he evens "feels" the food and if it does not feel right to him he will not eat it. So weird.
But have you tried muffins with him yet? My son will only eat Cinnamon Struel muffins(and I hardly put any of the sugary struel part on it). Since it's hard to have him eat "protein" foods, I puree zuchinis, mix the Carnation breakfast vanilla powder with the milk, eggs, etc. I have to load all the veg and protein that way. And he only eats the top part of the muffins. Try to slip in vegs that way. I would try to "sneak" foods in the foods he does eat. Does he like applesauce? If so, I take just a small amount of puree zuchini and mix it in with the applesauce. Enough where he cannot feel the texture or make it funny tasting. See if he would like to help you make lunch or dinner (like with the muffins). Keep on introducing new foods...one day it will happen. Even if he doesnt eat it put it on his plate so he sees it. I even have my son hand me his foods(like chicken nuggets, hot dogs, you know hard foods) that he does not want so he has to touch the food to hand it to me so he feels the texture. Spaghetti and squishy foods I dont have him pick up, we just leave on plate. For my son, big thing is for him to touch the food at least. Trying it is a different story but feeling it is huge. New thing with my son is he ate yogurt that he picked out by himself in the store. Saw Dora yogurt and wanted it. I asked him will you eat it? He said Yes. I did not think that would happen but got it. When we got home I gave it to him while it was fresh in his head...and oh my gosh he ate it! Even wanted more! He did not like yogurt before. So they need to make Dora on chicken, veggies, etc for me.. :) So keep on trying...
If the doctor says he's not underweight think should be ok and keep on trying. I know its frustrating but all we can do is hang on there.
I have a friend whos son is older than mine and is in the same boat with me and she tried the hard core way and gave him food and if he did not eat, he did not eat. To make the long story short, it did not work! He is still picky. As he got older he has "tried" new foods but still picky. I cant do the hardcore yet.
Well good luck to you and hope your doctor gives you some good advice.
Take care