Hello there, A history of diarrhoea that long suggests either an inflammatory or a parasitic cause. Considering your age both inflammatory bowel disease and diseases like lactose intolerance or sprue are possibilities. Also if you have picked up some kind of a parasite like giardia it can lead to diarrhoea like this. You need to get - Stool culture and microscopy done Blood -CBC including TLC D-xylose absorption test to evaluate any absorption deficits Please get these tests done and get back to me. I would be happy to answer further queries you have and discuss your treatment options.