yes. any antibiotic can reduce the effectiveness of your birth control. you should use other methods of birth control for at least one week after you completed the bactrim. when taking birth control and an antibiotic breakthrough bleeding is possible. probably the reason behind your worry!
i took bactrim for a uti while on my period; i am on low lowstrine. does bactrim affect birth control? . recently i have been spotting to the equivalent of a light menstruation. i have read that the bleeding during the middle of a cycle could point to pregnancy; however i do not recall my boyfriend ejaculating inside of me.