Hi I Have Been Getting Bleeding From My Bottom And

Hi I have been getting bleeding from my bottom and pain in my stomach and lower back. My movements are very sticky and i never feel like i do a full movement. I can go from having diahorrea to being constipated too. I had really black stools a couple years ago and was hospitalised but nothing was found, The doctors did x rays. Any suggestions what might be causing this as it flares up regularly. Oh almost forgot i sometimes get mucus when i wipe my bottom. thanks Lorna