What can cause bleeding between periods if you're on birth control? i had some ovary pain the night before, and i haven't missed any pills.

Hormonal imbalance: The uterine lining is responsive to progesterone and estrogen. Imbalance in the hormones can sometime cause irregular inter-menstrual bleeding. However, if its an isolated event, we can assess and evaluate in the future.

Several causes: Causes of irregular menstrual bleeding while on the pill include infection ( UTI OR STD) , pregnancy, antibiotic use affecting the efficacy of the pill, as well as uterine fibroids or cervical lesions. Noncompliance ( which is not your case) also is a culprit. If you have irregular bleeding and have been compliant with your pill you should see your doctor.