Still + ovulation test at 8dpo?

Hi I confirmed ovulation by chart on CD 12 and I am 8dpo! I have had Pos opks since day before O and they have been so dark they pull dye from the control line? Is my chart wrong? I know I don't have PCOS as I have has many different test, blood work ultrasounds HSG, ect. What could be the cause of this? I'm going on 10 days of positive opks. Please help!