You are in the growing age. Your height will grow more. So there is no fix limit, little bit + & - can be accepted.
It depends on your appetite that how much you eat?
You did not tell that how much is your weight now?
Then you eat less if you are constipated.
You eat less if your physical activity is less.
So try to play games & take 3, 4 small meals in the day. i think you will improve your habit .
You must take milk in your food it is very important as a source of calcium for you.
If still there are problems, take advice from your family doctor.