I'm Afraid I May Be Pregnant Although There Was No

I'm afraid I may be pregnant although there was no penetration involved, so I'm stil a virgin. A few times my boyfriend has only rubbed his penis on the outside of my vagina and since then, I've been getting pms symptoms which and very similar to pregnancy symptoms which is why I'm afraid. I've read about the possibility of pre-cum being and the sperm able to find it's way in this way, but how likely is that?