I recently had unprotected anal sex. Afterwards I went to the bathroom and noticed that the tissue felt really sticky. I looked down to realize that I had wiped sperm onto my vagina. I also either ovulated on the day before or after this incident. I took plan b 21 hours after this occurred. I am wondering how likely it is that I have conceived in this time period.

The morning after pill (Plan B), a high dose levonorgestrel (synthetic estrogen), is one of the most effective methods of emergency contraception. It has its maximum effect, up to 95% effective, if used within 24 hours of unprotected intercourse and is up to 89% effective if used within 72 hours of unprotected intercourse. For your reference, perfect condom use has a 97-98% effectiveness at preventing pregnancy.