C.O.
Try a different formula. He may be saying in the morning "Mom, I am hungry enough to drink this now, but later in the day I am not hungry enough to eat it and I really don't like it"
Be less concerned with quantity and more with quality of foods. Try some different (favored) foods and know that kids go through cycles. He may have a week where he doesn't seem to eat to much, and then he will eat everything in sight for a day or two. As long as he isn't losing weight or becoming apathetic, he should be fine. Just keep an eye on him.
Hang in there...