For about 2 years I did not have my period. They did hormone tests and found I was high in progesterone (the hormone that causes lactation) it was like my body thought I was pregnant.
It could also be ovarian cysts which are incredibly common. You may want to consider going on the pill to regulate your hormones. (But obviously talk to a gyno first)
My period did come back after I came down from 300 pounds to 285. How much that signifies I do not know.
The doctors never gave a solid answer for my lack of period.