Mom, hello, the child has diarrhea for the second week, I got sick two…

Mom, hello, the child has diarrhea for the second week, I got sick two weeks ago and since then the child has diarrhea, we have tried everything to treat it. We were prescribed special mixtures, nothing but breast milk wants to eat, occasionally there is biolakt. We sent it for analysis, elevated sugars in stool. The doctor diagnoses lactose deficiency. My father and I have this diagnosis from birth, but how did it appear in my child now, if it's mostly congenital pathology?