Hey, I Have Missed My Periods For Th Last Three

Hey, i have missed my periods for th last three months. I checked i am not pregnant. I have gained some weight and i think its because of missing my periods however, my doctor says nissing periods does not cause weight gain on the contrary it is weight gain that causes period. I just wanted to confrim that is he right. Also should i take premulot N just to start my periods and not tell my doctor as i believe he would object to that.