The lump could be a prolapsed
hemorrhoid, a skin tag, a benign rectal tumor, a rectal polyp, a rectal
abscess, or a hematoma. You will need a clinical examination followed by probably a STD panel or excision biopsy. Please consult your doctor for confirmed diagnosis. I can understand the embarrassment, but without a clinical examination by a doctor you trust, diagnosis and treatment is not possible. Take care!