Implantation, Late Period, or Early Miscarriage?

TTC for 5 months.  My period is 5 days late, but I've had 3 negative pregnancy tests this week.  Last night I had a little bit of brownish pink spotting and thought it might be implantation bleeding.  This morning the bleeding was a little darker but still not like my normal period - still more brown than red.  Also there was some clotting this morning, and I feel crampy especially in my lower back/abdomen.  Could this still be implantation?  Could it be a late period or early miscarriage?  So confused, and don't want to get my hopes up.