We ve been TTC for 9 months and even though the length from cd1 to O day varies for me.. i always get AF on 14 dpo. We had a chemical pregnancy last month.. then on the 15th of september i got a positive opk and we bd that day and the day after.. 14 dpo bfn, 15 dpo had 2 tiny spots of red blood when i wipped in the morning but then no AF and i never spot, 16 dpo bfn and no sign of AF .. dont know what to think..