I am 20, have long (approx 2 weeks) heavy, painful peroids and never had a pelvic exam. my mother had same issues and endometriosis, am i at risk?

Yes: It's time you were seeing a doctor, anyway. Go get checked.

Yes: Not that it's inherited but your symptoms suggest endometriosis. You need to see a good gyn physician, bleeding for 2 weeks & painful cycles are not normal. Not only do I recommend an evaluation and treatment, but this same treatment may preserve or improve your fertility for when you decide to have children. Take care.

Menses 3-4x/year: If you only have a cycle every 3-4 months, this may be another reason you have such painful cycles. The endometrium builds up and when the lining does shed (menses), the increased amount can cause prolonged & painful cycles. This also places you at risk for hyperplasia (precancerous endometrium) & you would benefit from an evaluation & hormonal rx (ocps, or Provera (medroxyprogesterone) for 10 of 30 days). Take care.