Crying 1.5 hours after eating


So Ive noticed my baby has a mini meltdown exactly one and a half hours after eating...every time. I'll try gripe water, gas drops, rocking, pacifier, etc and no matter what I do he cries for about 15-20 min and then it's over. It's puzzling. Does this happen to anyone else?? Any ideas what it could be? Hes been on nutramigen for milk protein allergy since 2 weeks (now 8 w) and is doing well on that.