I would like to trade concerns with you. You can have my constant, nagging nausea that only sporadically allows you to eat, and when you do, you may or may not get sick afterwards. (There is no way to determine this outcome prior to eating)
Really though, eat when you're hungry, stop when you're full. Only stop trusting your body's hunger signals if you start gaining weight *above a healthy weight*. (That is, if you're underweight, and you're gaining, then you probably are hungry all the time because you're underweight and you NEED to gain.) The only way you will every actually know how many calories you need in a day is to do one of those crazy metabolism tests at the hospital where you get wrapped in plastic and what not. And who wants to do that anyway?
And OregonAmy --> I wish Cracklin' Oat Bran was low fat. Man that stuff is good.