So about two weeks ago, I was messing around with my boyfriend. We didn't have sex, but I ended up giving him a hand/blow job until he came in my mouth. Being incredibly stupid and way too excited, I decided to masturbate soon afterwards, without cleaning my hands. I can't remember whether or not I touched his semen with my fingers before I masturbated, but I know that I had touched his precum.
What is the risk of my being pregnant?
My periods are completely irregular, sometimes coming after many months (my last one was May 3). I'm not on birth control. It's almost impossible for me to be able to go out and buy a home pregnancy test, since i don't live within walking distance to any stores, and my mother would almost definitely find out if i took the car (she would certainly literally kill me if she knew about this; she comes from a very conservative family). Even if i were able to obtain a test, with my irregular periods, I'm not sure when I should actually test for pregnancy.
I realize what I did was stupid; however, there's not really any way I can fix that now. I'm 17 and I haven't done anything like this before. This worry is keeping me up nights, and I have no idea what to do. Can you give me any advice?