What Causes Blood Filled Mucus Discharge Through The Rectum?

I have been having some bloody mucousy slimmy stuff squirting out my rectum before, during and after bowel movements, and sometimes when passing gas. There is also blood in the stool and around the stool. I been having abdominal pain as well with nausea, lightheadedness and dizziness for the past week or so. I went to hospital last night and all they did was take a stool culture and blood work and sent me home. said follow up with gi doc. i want to know what is causing this. should i be worried. Im also very bloated.