Why hasn't my period come?!?

I had sex for the first time about 3 weeks to a month ago. A day after i noticed it would sting and throb when I would pee. It went away after about a week. It came back on Tuesday. But I was supposed to get my period on the 23 of June and it hasn't come. We used a condom when we had sex. I feel a gargle in my lower stomach sometimes. Could I be pregnant? Why hasn't my period come?!