I am a 27 year old female not sexually active. A couple of years ago I started the Weight Watcher's diet and lost 100 pounds by eating healthy and have maintained my weight around 115 pounds. When my weight was 208 pounds my period was every 28 days like clock work. Now they are irregular. In fact, I have gone 4 months with no period. Is it due to my weight loss? Could it be something else?