Implantation bleeding?

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Hi everyone! My husband and I have been TTC for two months now. My last period started on March 31st. I've had regular periods prior to going on the pill (like clockwork) and have had regular periods since I came off the pill four months ago. 
My cycle used to be 28 days pre-birth control and 26 days since coming off of it. AF should have come today, but instead I've experienced spotting over the last two days. It's a brown colour and not very much at all. 
I started using OPKs this month and I should have ovulated on the 12th/13th. My husband and I did BD on both of those days. 
I'm wondering if this is implantation bleeding. It seems late, but is it possible?