Could be an implantation bleed. Remember that the eggie needs to be "attached" to you before you will get any symtoms/or a positive HPT. In that first week the egg is travelling down your fallopian tubes into your uterus, then trying to implant. This is why HPT recommend testing after OD7 (at the very earliest). It is also why you can get BFN then BFP. So it is a little early for symptoms, but about right for implantation. Hold off for a few more days (if you can) And good luck, only time will tell