Vagina cramps?

I'm supposed to start my period in 2 days and my boobs have been really hard and sensitive but that's kind of normal I guess. 
But yesterday I had really bad heart burn and then randomly I got a weird lower abdominal cramp. Like really low! Like felt down in my vagina and it was super uncomfortable it would last like maybe 5 seconds I literally felt like I was having a contraction😂 . It happened 2 so far but I've never felt those kind of cramps before my period ?? Has anyone felt that before finding out pregnant