Yes, I agree to ask your doctor. You could possibly have an overactive thyroid.
Plus, what some consider to be "a lot" of food can be very different than what others perceive it to be. Granted, you said people are surprised when they see how much you eat - but do you always eat that much, or maybe just when you happen to be around people? (For example, on the flip side, I have seen plenty of overweight people who never eat, or only eat salads, but obviously they must be eating something else/more at home.) Do you get busy and forget to eat sometimes? Do you have any idea how many calories you're eating per day?