Has this ever happened to anyone?

So I just had my period like a week ago , a little bit before that week I had sex with my boyfriend we use the withdrawal method . It's been a week like I said before and I woke up this morning feeling awful, my side was hurting and I was cramping like a period. It's nowhere near time for another period, but I'm having period pains, like my nipples are sore and I'm freaking out ! I asked him 2 weeks before the period I got did he "cum" inside me because it was a close call I actually think I felt it I dont know. I tend to over think everything!  But I'm asking has anyone ever had these pains after a period or could I just be pregnant. ( I'm 18 & we've been dating for 3 years )