There are many reasons as to why a person might never feel full, so it's best that you go get a professional opinion, see a doctor and rule out the possibility of things like diabetes.
It's impossible for us to answer this without knowing what your current diet and eating habits are.
Amypops is right about introducing more carbohydrates, as they are the most important food that gives energy. If you are not eating enough complex, long lasting carbs you won't have enough energy and will get very hungry all the time.
Try healthy rice, pastas, grains and breads - these things keep you full for longer compared to meat and vegetables.
But as I mentioned before, there are many other reasons as to why you are feeling hungry all the time, some can be symptoms of health problems, so be sure to see your doctor.
Otherwise, you might just have a fast metabolism. I also have a fast metabolism, and I find eating larger meals keeps me full longer than eating smaller meals frequently throughout the day. I make sure to eat plenty of carbs, which keep me full for longer.
If your not feeling full try eating slower and introduce more carb base food to your diet trust me it will help if you eat to fast it tricks your body into thinking that ur still humgry because of a hormone released by the stomach if u eat slower the hormone is stopped from being produced faster. Hope this helpedxxx