no period for 3 weeks. now possible miscarraige?

Faith

So my husband and I are not using protection but also not actively ttc, just trying to let things happen as they will. (Background we have 1 son who is 4 and before him we had a devastating miscarriage.) So my period is normally light with mild cramping and on a dependable 30 day cycle. However, this month missed completely. I've tested several times, with negatives. So I put it off as stress, and with this month being so busy I honestly put it out of my mind. I finally made an appt with my nurse midwife but that isn't for another week. And yesterday while driving home, I had very sudden, sharp cramps that made me catch my breath and jumped me off the seat. The bleeding seems moderate, no big clots or anything yet. Just wondering if anyone has any thoughts on this whole situation. I still don't want to say I was or am pregnant, because my last test 2 days ago was a solid negative.