You are quite right you do not know these forums.
It happens to about 20% of women at least once, most often in the doggy position. There was a study done in Australia's out it.
I can just think how painful it was, normally anal have to be done very very slowly and with huge amounts of lube and foreplay. your partner could also have damaged his penis and he was lucky that did not happen.
My suggestion will be to see your doctor if it does not stop. Your anus is not the cleanest of places (it's got nothing to do with you, just what happens there). It is important to not get any cut or tear infected. Did you take a mirror to see what happened? It will also be better to wash yourself clean with water, rather than wipe with toilet paper. Keep yourself very dry down there (cotton or no undies, pat yourself dry) Also try to limit bowel movements for a few days. The one positive thing is that that area heals pretty quickly. Use an NSAID painkiller like Ibprofin for pain management. An ice pack in a towel can also help to cool it down and reduce the pain and swelling.
Best of luck!