William is 8 weeks old and seen with his mother at the GP surgery. He was born at term by normal vaginal delivery and is being exclusively formula fed. Over the past 6 weeks she is concerned that he often cries and appears to be distressed whilst feeding. Mum says that he often brings up small amounts of milk. You note that he appears to be falling off his initial weight centile and agree with the health visitor’s concern that growth is slowly faltering.
William is not vomiting and is passing stool as normal. There is no blood in the stool. He had a cough and coryzal symptoms 2 weeks ago which was presumed to be due to a viral infection.
Based on the history, what is the most likely diagnosis?