@amysamp - The first thing you do is go to the doctor!! You could be quite a few things! I know for many many people it is an uncomfortable thought to have someone checking out such things, but I can tell you this much - it is common! So I hope you can find some comfort in that.
Since I have opened up about my hemorrhoids (to a few select friends) I have found that all walks of life get them from people who are pregnant, to weight lifters, to runners.
But I can't say it enough - go to the doctor - the rectum because of the waste involved is serious business.
If you do find out you have a hemorrhoid, I found two things to be very beneficial: 1) changing my diet & 2) using wet wipes instead of scratchy toilet paper.
I changed my diet by adding more fiber (think beans, vegetables, and fruit) and lots more water.
Since I have done this I haven't had a flair up, but I am keeping my fingers crossed because hemorrhoids are no fun!