I've had a similar problem though it was a one off for me last month. I went to the doc's for a blood test to see if maybe it was a BFP that didn't show up when I POAS but alas no. The doctor wasn't too concerned and said that a bleed was a bleed and she was ok with that and not concerned for our TTC progress. Unfortunately I can't say anything beyond that because I'm now back in the TWW again and hoping for 'something' positive in a bit over a week!

Sorry I can't help more than that but good luck, I hope you get your BFP really soon!