Very fast metaboliosm

Patient: I have very fast metabolism,i have very low weight, and i eat more,and i use many madicine to gain weight,but could not get.please prescribe me something to gain wieght.when i eat,at the same time i need to go into the washroom. and i think my stomach can not digest food a day i have to go 5 times ina washrom.plz help me

Symptoms: Fast metabolism