Please do not stress too much. I had the same thing happen to me. It could be old blood - particularly if you are using the pessaaries - you could have scratched yourself with your finger nail.
Anyway, as I said, this happened to me and I got a BFP!
Please just relax and take it easy
Barbs
Barbs - New Zealand. 33
1st IVF attempt - BFP BFP BFP!
Miscarried at 10wks 5 days