SOS - STD

TMI

I took my tampon out tonight and it had a large green spot on it. I can’t find any explanation for the color green other than an STD. I had unprotected period sex in April but I haven’t had sex since then and it only happened once. I also can’t go to the doctor (at least until I leave my parents after Labor Day) because we would have serious issues if they knew I had sex. I’ve had no other symptoms the past four months. Could it be anything else?