I have had a fissure before, and the doc told me to take warm baths, and use Anusol-HC. It is an over the counter ointment that you can purchase. Worked great for me, however, if it doesn't heal, you need to go to the doc and make sure that is where the blood is coming from.
The problem with any kind of rip in the anus is the threat of infection. I would not wait and try to self-medicate, because you don't want to get sick. Also please don't be too embarassed to tell the doctor things; believe me, they hear worse all the time, and it can be hard for them to diagnose problems properly if they don't know what it was. If you are really, really embarassed but want to come a little closer to the truth, you could say it was from anal sex without lubrication. But if you start telling stories about your diet, you might wind up on Metamucil or something and really it should be easier for the doc to know that it was an externally applied force. Good luck!!!!