My Boyfriend Has White Foam Coming From His Rectrum. He

My boyfriend has white foam coming from his rectrum. He has lost alot of weight in the last 2 years ever since he got his gallbladder out. He has stones that went into his pancreas and can't be removed because they are to big so the doctor said. He is a diabetic. He is also on blood thinners. What could be the reason he is losing so much weight. He weighed 305 he is now down to 125 he is 6 foot 2.