I read on this site that it is called breakthrough bleeding.
I had a HCG reading of 7 on Friday the day AF was due (13DPO) (doc said it was still positive but extremely early) - I was not showing up on HPT's at this stage.
Two days later (Sunday) AF showed up (which I thought was a sign of miscarrage as I assumed I was pg - Blood Test showed HCG level of 15 (15DPO) (Different Doc said this was a negative result and I was not pg).
Finished bleeding today (Wednesday) and got a nice BFP on HPT. The line started showing on Sunday but only very very weak and only with first morning urine. It is now showing up nice and strong today. Also was vomiting on Tuesday morning from 5am - 9.30am.
I am convinced it was my period because it must have implanted so close to when AF was due and I didn't have enough of the chemical in my system to stop it from arriving. I am feeling a lot better now but still a little on guard.
Please let me know if this has happened to you.
Thanks