Hi,
Welcome to the forum. I am really glad to help you out. Any chronic diarrhea needs to be evaluated. It can be due to deficiency of a single enzyme like lactase resulting in lactose (milk sugar) intolerance or it can result in generalized malabsorption like celiac disease or crohn's disease.
The latter 2 diseases are associated with diarrhea and weight loss. You'll need to undergo certain tests like serum iron, folic acid and vitamin B12 levels, serum proteins, serum electrolytes, PT/INR to look for the vitamin K deficiency, anti-gliadin and anti-endomysial antibodies to rule out celiac sprue. I'll suggest consulting a gastroenterologist.
I sincerely hope that helps. Take care.