Talk to Gastroenterologist on Unknown Diarrhea

Sir its been two years now that i am facing unknown diarrhea. It happens sometime due to milk and sometimes if i eat fruit alone.I am very much confused because one doctor in islamabad said that i have lactose intolerance and gave me medicine and His medicine which also includes lactase did not work.Then another doctor in multan which i discovered from marham said don’t eat fruits and milk.But,i was concious about my diet.So,i tried by myself.Recently about a week or two i was consuming 200 ml milk and was able to digest but not now.Now,i came to know about day fresh lactose free milk.At first,i digested the milk.But after about two to three consumption i am again not digesting even the lactose free milk.I am very very confused.And also sometimes i digest ensure and sometimes i don’t.Please help me.I want to gain height.I am an athlete.