what's causing this

so I had sex and he didn't put a condom on I asked if he pulled out he said yes but idk he even came bc things got cut short and I still took plan b, so week or two later I have my period its regular it's 5 days long and all but now I haven't had another period since and it's been about 3 weeks. I have NO symptoms or signs of pregnancy but the missing period, I wanna take a test so I can just rule it out but I am 16 so I'm embarrassed about going and I don't really have anyone to talk to about it, I completely regret the entire thing and I really need some guidance. another thing is I am in anxiety medications and supplements could that be affecting my period? and let's say I do get the courage to take a test and it's negative, should I ask to go to the doctor because my period is so late or just wait it out?