Weird periods

Alison
I have been having some weeeeird periods. We're ttc and this month I've had very light dark spotting for 6 days but haven't yet actually started (not normal for me) & am getting BFN's. My period is officially due to start on Sunday. 
Two periods ago, this happened and I spotted/had my period for a total of 22 days. Anyone have advice?? Planning to go to dr this month but was hoping for any advice you can offer, before then.