Welcome. To find out how much you should be eating, use the Tools on the Dr. Sears website (www.drsears.com). You tell it some measurements, and how much activity you do, and it will tell you the amount of protein (number of blocks) that you should eat for 1 day. Then you balance it with Carbohydrates and Fat, and you can space the blocks all through the day to be best for you. Usually 3 meals + 2 snacks, but it can vary greatly depending on your schedule and needs.
You can also feel hungry sooner than you should if the balance of your meal is different than it should be. For me, I also get hungrier if I eat the less favorable carboyhdrates like rice and potatoes and pasta.