My last period was 05/08,. based on an OPK, looks like I ovulated on CD12 (kind of early this month), then on CD18 I started spotting brown, which then turn red (but light),. then the last day was pink (it lasted 5 days)... I didn't really counted that as a period.
My next period was due yesterday (06/07), and it hasn't showed up, nor any PMS... but I'm having low back pain and some cramps starting 2 days ago...

I keep testing negative. Is there still hope?

Please see a physician he will be able to help you.