OTC tests are extremely accurate when tested at the right time. But if you are already 10 days late, I think I would give it another week or so and if your period hasn't come, or the OTC is still negative, I would go to your doctor.

Are your cycles irregular at all? If so, and your ovulation times vary greatly, you could only be a week or so from ovulation, and it would take a bit longer to show up on an OTC test.

What brand are you using, BTW? Clearblue easy is one of the best out there for detecting even the smallest amount of pregnancy hormones.