A lot of things can make you tired, but usually, it is because of your lifestyle choice. See Why you are always feeling tired:
1. Immobile lifestyle: If you do not move as you should, it could be the reason why you always feel tired. Workout from time to time, stand sometimes even when there is a chair close to you.
2. Lack of sleep: If your body lacks sleep, it cannot release the hormones that will regulate your energy levels and metabolism.
3. Not taking in enough calories: Even if you are trying to slim down, do not make extreme changes to your calorie intake in such a way that your body will lack what it needs to work at full strength.
4. Inadequate hydration: To make sure your energy levels remain high, drink enough water.
5. Too much stress: Even if stress is normal in life, too much stress will make you tired.