What Causes Delay In Period?

Okay. So I have a problem. I am a virgin, but my boyfriend and I do have occasional oral sex. His penis has been no where near my vagina and I don't recall him ever fingering me with semen on his fingers. I have been experiencing PMS symptoms for a week and a half, but still no period. Do you think that it's possible that I'm pregnant even though I'm a virgin and his penis was no where near my vagina? This is probably a really awkward question, but I just want answers because I am so sick of worrying.