I have pencil stools, blood in stool, constant diarrhea/constipation, sharp pain in my bottom left side, fatigue, & mucus in stool. what could it be?

IBD?: Blood and mucous in your stools = go see a doctor! Infections can cause this. So can inflammatory bowel disease, like Crohn's or ulcerative colitis. I don't know your age, but if you are over 40 then colon cancer is also on the list of possibilities. Your doctor will probably check your stool for infection, and might want to do a colonoscopy. You need to feel better! A diagnosis is important.