9 Days Late.

Me and my boyfriend had sex for the first time around January 21st last month. We used a condom and it did not break. I am not on any other form of birth control, and my period is now 9 days late. My period was a week late last month for the first time and we had sex after i got off of my period. My period is normally regular but it was a week late last month and now 9 days this month. I am a little worried. But last week i took two pregnancy tests and they both came back negative. I have one left so when is a good time to take it? I have been very stressed because of the situation lately and maybe that is why my period is late? Im not very sure. Could i be pregnant? This was my very first time having sex. Am i just being paranoid?