Pregnant? Super irregular period?

So, my period is late for 16 days and I'm kind pretty scared, I had sex for the very first time a few months ago, and since then my periods have been super irregular (that's what keeps me a little calmed)

First question: could start having sex affect my cycle? When I was younger I could skip my period for months, and then I went to the gynecologist and she found I had a little cyst so she put me on the pill to regulate the pill and dissolve the cyst.

Second question: I had sex for the last time around a month ago. We used condom and made sure it didn't rip. Is there any chance I'm pregnant? I haven't had any symptoms but what confuses me is what I've been having white discharge which scares me because some people say it's an early symptom of pregnancy and some say it's because your period it's about to come.

Please leave your thoughts below. I CAN'T be pregnant, I'm only 18 and having a baby right now would not be good.