S.B.
Try weening him slowly. Give him 3/4 formula and 1/4 milk mixed together for 2-3 days. Then 2/3 formula and 1/3 milk for 2-3 more days. Then 1/2 and 1/2 for 2-3 days. Then 1/4 formula and 3/4 milk until he takes the milk without formula. I had to do this with one of my boys. It worked for us. Hope it works for you. Good luck.