I agree with Joy....both of those parts are very close to each other and chances are he would have touched the vag at some point. The chance is there. Wait your four days and take a test if you're late.
It IS possible to become pregnant from anal sex as there is very little separating the vagina and rectum, not to mention semen can seep out and down to the vagina. You can take a pregnancy test to see if you are pregnant or not.
I know this is a serious topic...and I agree with Ashelen 100%...but I had to LOL@ pooper...even the wonderful boyfriend got a good laugh!
There's very little chance that you got pregnant from anal sex. However, if you did not use a condom you have a very high risk for infection. There are a lot of close-to-the-surface blood vessels in the anus and if they're irritated they can easily become infected. This sort of bacteria can be easily spread to your vagina or bladder when wiping after a bowel movement, or even after urination. You should always use a condom when having anal sex to prevent infection. If the symptoms you are describing do not go away when your period starts, you may want to see your doctor to be tested for a vaginal infection, because it can cause those symptoms. if you start getting a strange vaginal discharge (smellier, heavier, or darker than usual) you need to see your doctor asap to be given a pelvic exam to check for infection. hope this helps :)
(i know that some women and men enjoy anal sex but I, personally, would recommend not performing it because it carries such a high risk of infection, and even with a condom you can seriously irritate a very important part of your body....your pooper!)
but I think a very low chance of pregnancy.