I think I have a rectal prolapse since I gained 20 lbs. Could it be from that?

Unclear. Weight gain can put more pressure on many areas of the body, including joints as well as the pelvic floor. Tissue prolapse in the anal area may be hemorrhoidal; you will need to see your physician for diagnosis. Weight gain may cause a true rectal prolapse to become more apparent, but cannot cause a prolapse if none was present before.