Feeling hungry constantly even after eating is not normal and you should see a doctor about it.
You could have what's known as a Leptin Resistance.
Leptin is a hormone that is produced by your body fat that controls whether or not your stomach feels full after eating.
You may also have Hyperthyroidism which is a condition that is characterized by an overactive thyroid which can also cause you to have a constant hungry feeling.
So you should certainly get checked out by a doctor especially if you're always feeling hungry even after eating.