Hello, Pregnancy is possible only, if unprotected sexual intercourse is done with ejaculation around ovulation time in regular period. Sometimes precum or prostatic fluid,secreted prior to ejaculation, causes pregnancy in low percentage but it also depends on fertile days. In your case, as you took contraceptive pill on regular basis, then chance of being pregnant is very minimal. It has effectiveness more than 99% in preventing unwanted pregnancy. For better confirmation, you can do a blood test for beta hcg or ultrasound scan as your period is skipped. After that, you can consult with your doctor. Avoid stress, take healthy diet and practice safe sex by using safe period/OCP/Condom etc to avoid unwanted pregnancy. Be well.