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If semen or pre-cum has come in contact with vagina during sexual contact, (condoms can have failures), chances of pregnancy are possible (chances are high if you were closer to your fertile days at the time of sexual contact). The symptoms that you describe (delayed periods, abdominal cramps, heartburn) could indicate early symptoms suggestive of pregnancy. Wait and watch for your periods. Look out for development of any new symptoms if pregnancy is suspected. Visit your gynecologist for further evaluation and assistance if you do not get your periods within 10 days of expected period dates, or if you get abnormal bleeding. If pregnancy gets ruled out and if you are not ready for pregnancy, but intend to remain sexually active, you should consider getting started on suitable regular birth control measures to be protected (after periods). Be regular with birth control use as instructed. Avoid having unprotected sexual contact if you are not ready for pregnancy.
Take care.