I'm not good at tracking my period...

I am really bad at tracking my period and I don't really know how long my cycle lasts because of that. However, I'm trying to figure out if I am possibly pregnant. I had unprotected sex Oct. 20th, using the pull our method, and my last period started somewhere around Oct. 10th and ended about 5 days after that. If anybody could give me any opinions, that would be extremely appreciated... I'm really nervous.

Also, when should I take a test? I don't really know an exact date of when my next period should be, so I don't know how to tell if I'm late.