You should take another pregnancy test in a few days, if thats still negative, then i suggest seeing a doctor. You could possibly be pregnant, but the HCG isn't high enough for the test to pick up yet.
hey, let me know if you found you are or not, i have an appointment on the 15th as well, which is when i'll find out too haha
Antibiotics, infection, stress over thinking you're pregnant- these can all contribute to a late period. Just because you have sex during ovulation doesn't mean you'll always become pregnant. I would take the tests at face value, treat the infection and go from there.
If your so worried about pregnancy...why aren't you using protection? Anyways, anytime you have unprotected sex you can end up pregnant. Stress will delay a period as well. When you go in for your check up, tell them you might be pregnant and they will give you a test.