I know nothing about rectal melanoma, but perhaps is same as anal melanoma of which there was a previous posting on this sight which may be a place to start for info on symptoms of rectal melanoma. It was posted on 8-21-09 by Nancy titled anal melanoma. I think any symptoms your body is giving you would be reason for a doctor to check it out. My knowledge of melanoma is to get yourself to a treatment center specializing in melanoma.....run . . . do not walk. Praying for you!
Sunnydae