There is a product called "egg Replacer" you can get from whole foods or the health food store. You use it in baking (cookies, brownies, breads, meat loaf, etc) It works great. It is a powder made from tapioca/potato starches.
I am guessing even as a busy mom, you will need to make specialty things for him.
As far as being picky, he won't let himself go hungry... keep feeding him appropriate healthy foods. Banana w/ Peanut butter (or almond butter or chocolate peanut butter) is filling & loaded with protein. Most kids love it.
Use a cookie cutter to make fun shapes out of sandwiches, quesadillas cheese etc.
The cookbook "The Sneaky chef" has been helpful to my friends with picky eaters.
Hang in there, he will go through many changes & you will survive them all!
P