I Have Had Diarrhea For 3 Weeks Not Eaten Much

I have had diarrhea for 3 weeks not eaten much lost 13 pounds if I do eat within one hour I have diarrhea and it is green not runny but consistency of maybe ketsup. Pain in lower left pelvis. Light headed and dizziness most likely from not eating. Even when I don't eat it still comes out muscle is totally gone. I cannot even feel it coming out. Have not felt well for a couple of months. Thank you Barbara Wurn