brown discharge and frequent urination

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If you have been regular with your birth control pill use and have not missed taking pills, you should remain protected. However the chances of contraceptive failure cannot be ruled out completely. Sometimes you can have 1-2 missed periods while being on hormonal contraceptive pills. If you suspect chances of pregnancy, you should consider visiting your doctor/gynecologist for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). Look out for development of any other new symptoms if pregnancy is suspected. Urine pregnancy test kits usually start showing positive results after about 20 days post-conception (roughly corresponding to about a week after your missed periods). Sometimes urine pregnancy tests can keep showing you false negative results during early pregnancy as the kits are calibrated ones, so unless the hormone levels in urine reach a certain level, they do not show positive results. You might also consider taking a urine pregnancy test (on an early morning first urine sample) after 7-10 days (if you do not get your periods within 10 days of expected period dates) to see if you get positive results, or get it confirmed by a blood HCG test (avoid lot of fluid intake or caffeinated beverage intake in the previous night before test). Stop the birth control pill use if pregnancy is suspected, or if pregnancy gets confirmed.
Take care.