Nervous about pimple down there

So I have only have one sexual partner and it was only once 3 weeks ago. We did not use a condom. Today I had a huge white head down there on one of my lips and it popped. Should I be worried? It was just one and there do not appear to be anymore. I'm just worried because I am afraid I could have an STI and I don't want my mom to know. I am 18 so I can go to the doctor by myself but I am just nervous. Should I be worried?