Why do I keep getting hungry today?

I'm a teen girl, and for some reason, I've been hungry pretty often today. I added peanut er to my oatmeal & banana this morning, so I thought that would keep me fuller than usual with my mid-morning snack (140-cal South Beach Diet bar) and lunch (potato-tomato sandwich & 1 red apple) still eaten as usual. At around four, I ate two plums, one True North nut cluster, one tiny slice of dry fruit. I was still hungry an hour later, so I drank 1/2 a cup of OJ, one small pretzel, and another tiny slice of dry fruit. But I'm still looking forward to dinner! What's going on? My first thought is that I'm growing, but I'm kind of older in my teens and it doesn't seem like that should happen to me anymore. Don't hunger pangs like that happen in your lower teens?