Missing period

No sign of my period. Ive been 5 days late. Last time we had sex which was protected was july 3. I took a test on the 25th after my missed period (i posted that too) and then i took a test now 5 days later and still negative. Pls tell me its accurate. Its been 25 days since the contact that was protected so like 3 weeks and i got two negatives but no period.