If it's worrying you too much why not try to keep a little log / notebook to check and record your weight each morning before you get dressed or before you have eaten.
Then look back over the records for say, 2-3 weeks and see how your weight has fluctuated. You might find that although your pant size is getting smaller, your body fat is distributing itself elsewhere - like in your upper arms, for example and that your overall weight is not changing greatly.
It is also worth avoiding the routine of eating loads and loads until you are stuffed full.
Your body may be accelerating its digestion to deal with large quantities in one helping and that is why you are feeling hungry again so soon after.
Try to regulate the amount of food you eat at one sitting and perhaps eat one extra meal during the day - so that they are more evenly spaced.
If you are sure there is significant weight loss and you are not overweight or dieting you should speak with your parents about it and ask their opinion. They may suggest a check up with the doctor.
Whatever the case, a little "weight" log will be useful to show them or the doctor.
If I were you, I would probably go to the doctor if the problem persists. And remember to keep track of the things you eat and the KINDs of things you eat. 
