Thank you for posting your question here, I will try to answer it to the best of my abilities.
It is possible that you are suffering from hemorrhoids and that is what is causing the pain in your anal region. As for the leg cramps
, do you have large veins visible on your legs? If yes, then it is possible that you do have varicose veins
and when someone has varicose veins they should avoid sports, this includes cycling.
I recommend you see a doctor, so that he can give you a general examination and confirm the diagnosis. Mind you, I could be wrong in my assumptions here, as I am basing them on what you have said without seeing you in person.
I hope this answered your question.