Delayed periods and had contraceptive

I had a I pill on 13th may and my last period dates was 18th may normally i have early periods this was the first time I had i pill and today is 18th but i still didn't got my periods i am kind of sure that I am not pregnant as it was a protected sex and still I had a I pill but still I am worried about periods can you prescribe me something which gets me immediate periods I am a student so I cant even consult a doctor