I am 21 and have pain in my lower left abdomen every month between periods, for the past 2 years. Do I have ovarian cysts? Do I need to see a doctor?

Could b a cyst. It is hard to be sure. I would expect a persistent cyst that has remained present (not coming and going) for 2 years to cause a more persistent type of pain, but it is a possibility. Could be due to endo-metriosis (but that usu causes pain leading up to and thru the period). Could be due to scar tissue. Or could be a nerve pain originating in the pelvic region, hard to dx. If pain is bad:see dr.
Visit MD. It is a good idea to see gynecologist at least once a year. Your are more then 2 years behind. Doctor will help.