Lower left side pain after sex, what should I do?

I just had sex 4 day's ago and I'm having constant pains in my lower left side and I'm scared I might be pregnant. We didn't use a condome but he never finished inside of me. I just lost my verginity and I didn't bleed. Today I'm just having pain that feels like PMS. I should be starting my period in the next week or so but is that why.? Or is it because it was my first time.