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Condoms are associated with failures. If semen or pre-cum has come in contact with vagina (during foreplay or chances of semen spill while removing the condom), chances of pregnancy are possible. If fertile mucus had been present at time of intercourse, sperms can stay alive for 5-7 days and fertilize the egg upon ovulation. After ovulation, egg has only 24-48 hours to get fertilized. Look out for development of any other new symptoms if pregnancy is suspected (early pregnancy symptoms and PMS symptoms can be similar). If you missed your periods, or if periods have been abnormal/lighter, or if you suspect chances of pregnancy, consider visiting your doctor/gynecologist at the earliest for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). The altered discharge that you describe could be attributed to implantation bleeding (if you are pregnant), or to breakthrough bleeding. The discharge could also be a result of endometrial separation caused by uterine contractions due to orgasm. Stop the use of hormonal contraceptive if pregnancy is suspected, or if pregnancy gets confirmed.
Take care.