11-12 DPO and cramping!

Due for AF on Sunday.. I'm currently 11-12 DPO and I'm having serious cramps.. Woke up this morning and I was spotting, very minimal, barely anything on the panty liner and it was brown (tmi sorry!) I took a test yesterday and this morning both clear negatives. Could the spotting been implantation bleeding? Also, when should I test again or just wait to see if AF shows?? Thanks ladies!