If you want to lose weight, common causes of weight gain like overeating, lack of exercise,
diabetes, hypothyroidism have to be ruled out
in your case. You must then look for other causes. One is water retention due to low serum protein. This along with anemia can cause unexplained weight gain. Adrenal gland problems are the other cause. Cushing’s syndrome should be looked for. The kidney function too should be assessed. Late night snacking and poor sleep too can cause weight gain.