How fast it is going? Is it in the middle 100s or over 200? Does it start and stop in one beat? Have you had blood work to test your electrolytes and hormone levels, especially thyroid? Since it coincides with your period it could be hormone related but I would suggest seeing your doctor for a full physical and see what comes up. I would also highly recommend seeing a gynecologist if you are having discharge in between periods. For now try to drink lots of water. That seems to help the heart function better. Take care. I hope you can get to the bottom of this soon.