Thanks for the query to H.C.M.Forum.
Bad smell stool with excessive amount is not due to any disease.
Main cause of this is due to overeating.
If protein is taken in food in excess amount , it will develops bad smell stool with expulsion of gases through anus ( fart
As you mentioned that every test is normal , so need not to worry ,rather change the diet
and its ingredients .
Take in limit with more fiber
Vegetables should be taken in excess.