what is the difference between menstrual cramps and early pregnancy cramps

Im 6 days late, negative test yesterday. But last night i was cramping and it was radiating towards my back literally all night. The cramps were mild and bareable but just uncomftorble. I want to know from your personal experience if you had this prior to bfp, or just period coming soon. I am 6 days late so this is not pms.