Birth control and unprotected sex

so I have been on the pill for roughly 17 years however in the last week I have may be taking my pill late in the day 2 days. I have been dating a man for three and a half months and we had unprotected sex I'm not sure where I was in my ovulation cycle how soon is a pregnancy test accurate? I have taken two that were negative but some people tell me I will not know until I have actually missed a period. thank you for your help!!