Reduce the Milk intake. Could be Lactose intolerant.

It's probably food related. When my son was younger and even sometimes now it happens. Pay attention to the food intake.

G has always had problems. My suspicion is gluten. He is finally trying a gluten free diet now at 19. (Maybe not 100% free, but a start.)

Very common among children with autism. Sometimes this can be an easy fix. Ask your doctor to check for food sensitivities and gluten sensitivity. Best of luck!