What medications are you on. Antidepressants, Bipolar meds... Many of them inhibit the ability to lose weight... or
Are you or were you ever anorexic, bulimic? If so, this may have slowed your metabolism way down.
These are two things that have an effect on proper and normal weight loss. Also, diabetics have a problem as well. There are many factors... really.
Talk to a specialist, which is a Metobolic Doctor, that is educated in testing and treating the metabolism.