My period is 3 days late with negative tests. How accurate?

Hello,

I have posted on here before and i do it again because I find it helpful to get others opinons.  I am three days late on my period.  I had unprotected sex on the day I ovulated.  All the Hpt tests (including one i took yesterday when i was two days late) have come up negative.  I had a blood test at the dr. last week 10 dpo and that was negative.  I am concerned because I am on some medications that I may possibly have to get off if I am pregnant.  My husband and I did not plan to have this happen, but now that it has I am hoping for a happy little accident.  I have had cramps almost every day for two weeks and some nausea.  I had bad cramps exactly 7 days after ovulation.  How accurate are these Hpt tests?  I am finding lots of stories of women who didn't get their positives until weeks after a missed period.  Should i go back into the doctor for a blood test again next week if it doesn't come?  I am really concerned about the possiblity of being pregnant on my meds. Thanks so much.