Constantly Hungry?!

Ashley
I recently started trying to get healthy, loose a little weight, the usual New Years Resolutions lol. 
So, I've been trying to keep track of my calorie intake and exercise more, and surprisingly I've stuck to it and it hasn't been as hard as I expected. 
But, I'm constantly starving. I can literally eat an entire large pizza (by myself) and be starving two hours later. 
Is this normal for a person who goes from almost no physical activity at all to exercising every day?