Since you are sexually active, you need to get this checked. Do not try and pop it anymore and let the doctor see it as is.
Its most likely a pimple, but you do need to get it checked. Go to an std clinic if you aren't comfortable going to your regular doctor. They can check and treat you, if needed, and can't tell your parents.
Aj
By the way, i only had unprotected sex once and that was about 1 and a half years ago.. and the last time i had sex was about a month ago..