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Extreme changes in exercise levels, diet, lifestyle could delay your periods. If you had been sexually active and pre-cum or semen has come in contact with vagina, chances of pregnancy are possible. Visit your doctor/gynecologist for further evaluation if periods do not start within 10 days of expected period date, or if you suspect chances of pregnancy, or if you develop any other new symptoms. If pregnancy gets ruled out, and if you are not ready for pregnancy, but intend to remain sexually active, you should consider visiting your gynecologist to get started on suitable regular birth control measures to be protected (after your periods). Be regular with birth control use as instructed. Avoid having unprotected sexual contact if you are not ready for pregnancy.
Take care.