My period is pretty regular.cycles are about 36-38 days long.i am now on day 50 with no period, so 11 days late. neg urine preg test at 5 days late&neg blood test at 6 days late. light cramping, back pain, more discharge.feeling off.what could it be?

Irregular menstrual periods are common. The fluctuations of estrogen and progesterone can be easily affected by stress, weight gain/loss, exercise, lack of sleep, thyroid problems, and uterine issues. If your period irregularities persist, talk to your Dr about what testing can be done to determine the cause. If you have had unprotected sex, doing one more test one week later should confirm status

Menstrual irregularities are not uncommon and anovulatory cycle is a common cause. If you miss more than two periods it would be time to see your doctor. If you do not wish to be pregnant, use contraception all the time. You may consider implanted contraceptive or an IUD. Consult this site. http://www.nichd.nih.gov/health/topics/menstruation/conditioninfo/Pages/causes.aspx Get HPV vaccine.