No period in 7 months, not pregnant.

M
I have not had my period in 7 months. No, I am not pregnant. I am 20 years old. I have done some research and based on what I have read I have Amenorrhea which means that I have not had my period in over two months. I have gone to the doctors twice about this and they have given me zero answers as to what could possibly be going on all they have done is taken pregnancy tests. I am going to go again to get some blood work done being as an absent period could be a number of things from hormonal imbalances, cysts, or even a tumor which is what my boyfriends mother had on her pituitary gland. Have any of you ladies experiences this or something similar where you missed your period for several months but you were not pregnant? If so please comment down below! Thank you in advance!