Every time I eat milk products my stomach is in pain for days what could it be?

Lactose intolerance? Lactose breath testing (objective) or a clinical response to lactase enzyme supplements ;/or milk avoidance (subjective decline in the gassiness ; diarrhea associated with ingesting lactose) may clarify your concern. Some (particularly children) with suspected lactose intolerance however are intolerance to other milk components. Bleeding, weight loss, significant tenderness is not lactose intol.