Decreased Appetite. Done growing or something else?

I am almost 20 years old (female) and over the past few months I have begun to notice that my appetite has decreased slightly. During my teen years, I could eat a LOT of food! I was always skinny (technically underweight) but since going on birth control pills (2 years ago) I have gained just a little weight and now I am a very healthy size. I have no problems with my weight and no desire to lose weight, but now I can only eat small portions of foods I once ate large portions of! For example, when I get fast food, I can eat the burger, but have no room afterward for the fries. It isn't that I don't eat, I just don't eat AS MUCH in one sitting. I still get hungry throughout the day and eat a small snack but then I'm full for a while until I'm ready for the next small snack. I've also realized that I can no longer eat as much sugary sweet stuff as I used to. I can't finish a whole cupcake without feeling sick. Is my body just acting normally because I'm done growing? Is my metabolism slowing down? Or do I have a bigger problem? Again, I want to stress that I am eating enough food, just not as much as I did when I was younger.

[ticked]

Have you tried getting tested for Celiac?