I used to get my period on a regular basis for years. As i got older i began to miss my period for months at a time. I am 18 years old and under an extreme amount of stress. I have no gone 8 months without a period, potting or any abdominal pain. I have taken several pregnancy tests and they have all come out negative. Now i am beginning to experience brown vaginal discharge and small amount of abandoning pain. What causes this and should i be concerned?