I've been on the same birth control for years and have only had sex without a condom for the same length of time. I have experienced a lot of symptoms since I've had sex with my boyfriend right after taking antibiotics for a supposed UTI. I started experiencing a lot of pain in my lower abdomen after skipping around with my pills and then some really heavy dark and clumpy bleeding came. I got my pills back on track but now that my period time is here the very heavy and even thicker bleeding has come back and the flow is relentless!