Lower back cramps 5DPO

I am having these really bad period like cramps , it started low in my abdomen and now it’s sitting in my lower back. Also , a feeling like my uterus is heavy i don’t really know how to explain the feeling .. I remember having bad cramps on one side with my first pregnancy around 6dpo where I know is the earliest implantation can happen . Is it possible I’m pregnant again ? I know it’s too soon to tell but who has had cramps low in there back and resulted in bfp ?