Implantation bleeding??

Laura
Help ladies.. I BDd on cd 8 and cd 10. I'm now on cd15 and had some dark
Brown / red discharge last night which looks like when AF is due. I'm
Normally around 28-33 day cycles so it definitely can't be AF.. I've been testing for positive opk since cd 10 but all negative. Is it possible I Od early this cycle say cd 7/8 and this bleed is IB???? XXXX 
Sorry if it's TMi but this is the pic of the bleed which I've never ever had before at all xx