What Causes Missed Periods Since 10 Months?

Hi I am 20 years old. I haven't had my period in ten months. I haven't had sex in 3yrs.I have never been on birth control. I have never had kids.My mother and some woman in my family do have a history of tumors but there symptoms were very different from mine. I have been under a lot of stress. And i am overweight i am 5'6 and 220. I really need some help. I don't have insurance and free clinics don't pay for everything.