pregnancy??

So last night me & my boyfriend had unprotected sex. While I was on top he groaned as if he had came, but when i went to look there was nothing there. & he said he felt like he came but he didnt?? After i went to use the bathroom I tasted his nut when i sucked him so I feel as if he did cum. My period is suppose to be here tomorrow, but im very uneasy. Should I buy a plan b? or can I even get pregnant?