You need to be seen by a doctor if it has been several days and you are still experiencing the amount of pain and discomfort that you described. Be candid and honest with your doctor and tell him/her about your previous anal intercourse activity. As Dr. Danny said, the doctor might blush when told about your anal intercourse activity. However, most doctors don't easily blush given their extensive medical training and knowledge gained from many, long hours of practical duty in an emergency room early in their medical careers. Whatever personal embarassment you might feel about disclosing your anal intercourse activities to a doctor must take a backseat to medical necessity and deep personal concern about your physical health.
Oh -- and next time, do use lots of lube and better judgment when bottoming for your next rectum assault.
NOTE: I get an annual Class I Flight Physical which is very comprehensive and thorough. My doctor is a female Flight Surgeon and I can attest to the fact she does not blush easily given my medical history and her personal knowledge about my sexual history as it relates to my physical health.