Hello, Thank you for your query. Yes intense exercise can cause hormonal imbalances that delay periods, reduce menstrual flow and even prevent ovulation if too intense. As your pregnancy test was negative 4 days past your due date and you used protection, pregnancy is unlikely. Other common causes of delayed periods are functional ovarian cysts, sudden weight loss or gain, major lifestyle changes, illness, travel across time zones,anemia, Thyroid hormone imbalances. Vaginal infections do not delay periodperiod, I I recommend : - an OBGYN consult -ultrasound pelvis to rule out cysts -blood tests (complete blood count, TSH, free T3, free T4,) reproductive hormone levels, if indicated -swab of the vaginal discharge and antibiotics if it is an infection Based on these results, a treatment plan will be formulated. An ovarian cyst, if present, usually doesn t need treatment unless more than 5cms or persists more than 3 months. I suggest that you exercise with moderate intensity and slowly work your way up in intensity. This will help body adjust. If your are a professional athlete or are involved in strenuous activities routinely, your period may continue to remain irregular. Hope this helps. Please let me know if there is anything else I can help you with. Wish you good health