Can someone please read & give an opinion!

Just had sex with my fiancé, we've been trying to another baby on & off & yes lately be has been finishing in me. Other times that we've had sex & when he would finish in me, I'd feel just fine, even after doing it doggy. Tonight, we did it doggy again, this time, I feel different & have a little mild cramping.. has anyone gone through this & then ended up being pregnant? My period isn't suppose to be here until September 15th.