What could a lump on my rectal area that itches be if 3 doctors have said its not a hemorrhoid?

This is probably TMI but I thought I would ask. For about 16 months now I have had moderate to severe constant itching on my rectal area. There has been bulge that has formed there too. Sometimes it bleeds. I have had 3 doctors tell me its not a hemorrhoid and I had a colonoscopy that came out clear. What could this be? It is driving me crazy.