a lump can be piles or hemorrhoids or prolapse.
the cause of these can be hereditary to lack of fiber in your diet.
i would advise you to consult a general surgeon
regarding the same who will carry out certain tests like a proctoscopy and will be able to diagnose the same.
the treatment will be based on the diagnosis. it can be medical or may involve a surgical procedure.
in the mean time i would advise you to eat fiber rich diet, have plenty of water and regular moderate exercise.
i hope i have answered your query,
take care and i wish you a speedy recovery