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.
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.
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
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.