I saw a story like this on tv once. The way they helped introduce new foods was to add one ingredient to something they already liked eating. For example, say you like just a plain sandwich, and dont like vegetables on it, try just adding a piece of lettuce, or a slice of tomato. Or you like just plain pizza, add a little bit of bell pepper.
Definitely think you should seek professional help though, its a lot easier when you have someone to guide you!💖💖