my digestive system is funky too , i put mine down to IBS , cant have gluten , lactose , onions , garlic to name a few
BUT I can eat yoghurt and have ZERO side effects.....must be something to do with the good bacteria and all that.
Im not too sure how to officially test for lactose intollerance but ya doc might.......at the end of the day its just trial and error as to what works and what doesnt.