You may be trying hard to do all the right things:

→   starving yourself on diets and struggling to resist your favorite foods;

→   You are so motivated and serious in your desire to lose weight, being overweight makes you feel unhappy;

→   You keep trying because you do have a real desire to look better, to be healthier and to be in control.

Some people are overweight because of physiological reasons such as low thyroid activity or a very slow metabolism, but most people who are overweight are simply taking in more calories than they really need to.
Consciously you want to lose weight and stay slim. The reason you are unable to do so is that your eating habits are not determined and controlled by your conscious mind, but by your subconscious mind. Your subconscious mind is powerful and is responsible for habit behaviours, as much as you try to exercise willpower with your conscious mind the subconscious will undermine and resist that unless changes are made at the deeper subconscious level.