The glands that produce hormones in our body comprise the endocrine system. Too much or too little hormone production can cause problems with weight gain or loss as well as skin changes including excessive hair growth. For instance, excess production of the thyroid hormone, can lead to a loss of periods as well as weight loss. Too little thyroid hormone (hypothyroidism) can lead to weight gain and heavy periods.
There are many other less common causes for weight change. If the problems persists, you should seek medical advice.