LACK OF SLEEP: When you don't get enough sleep hormone levels in your body changes in a way that increases hunger and appetite.
STRESS: The perfect way to gain weight. When you are stressed your body releases more of the hormone cortisol, which causes a greater appetite. The risk that you grab for anything in reach when you are stressed is also a factor as why people under great stress often gain weight.
HYPOTHYROIDISM: If your thyroid is not making enough thyroid hormone, the metabolism slows down and causes weight gain along with tiredness and weakness.
MEDICINE: Certain medicines can cause weight gain due to fluid retention and change in hormone levels. Speak with your GP if you take medication that you believe might cause weight gain.