16 years old, having problems with my period. The specialists suggested a birth control pill to help regulate them. I have been on them for a few months now and I am irregular. I have had blood work and ultrasounds that are all negative except for my B12 is low. I am now on my 20th of my period. I have and undiagnosed pain on my right abdomen that is confirmed not the appendix. I have never been sexual active.

First I would go to another doctor and get the pain diagnosed. Could be a cyst or something. Also extension worry can cause long periods, but it's not good, that is your blood! The b-12 was given to you because you must have had high blood pressure or showed signs of stress, I would advised to take it and maybe stay off coffee, sodas, chocolates also as they make you anxious, hyper and make your heart beat faster. If you are in a stressful situation, get away from it because it is doing you harm. Planned parenthood is very good and usually free.
Good luck sweetie and please don't let this go on any longer, do get help. Please!