Ladies, a question

It's called Exercise Induced Amenorrhea...Heavy or strenuous exercise, including intense sports such as ballet dancing, gymnastics, Olympic-length triathlons and long-distance running, can trigger spotting in between periods. Strenuous exercise can slow or prevent the release of GnRH, which is a type of hormone that tells the body when to start its menstrual period. The combination of extreme exercise and low body weight can cause the body to go into a “starvation mode,” in which it starts to shut down organ systems, including the reproductive system. See a doctor for a diagnosis he/she can rule out any other medical conditions and complications. In the meantime, listen to your body while you are exercising. Slow down if you feel you are pushing yourself too hard. Reduce your exercise levels to 150 minutes of moderate exercise a week, such as a 30-minute bike ride five days a week. Or you can do 75 minutes of vigorous exercise a week, such as jogging for 35 minutes three days per week. Perform exercises that reduce stress such as yoga, Pilates or martial arts at least twice a week.

Do you have an IUD or are you pregnant, perhaps? I can't think of any reason why exercise would do this. You should see a doctor.