Why do I have under eye bags and dark circles?

I'm 15 and I get enough sleep. I go to bed, and have for ages, at about 10 and wake up at 7. But when I wake up, without a doubt, I will always have puffy under eyes and massive dark circles... I don't know what this means, but I'm sick of looking like a zombie. I don't know if I have a health problem or something? I have no allergies which could trigger this problem, and my parents don't have them, so it's not genetic. Although I get enough sleep, I am always tired throughout the day and my friend thought that I was anemic so I have started taking an iron supplement, this seems to be working in making me feel slightly more awake, but I don't know if they're a good idea or not? My mum thinks I could be 'over tired' by getting too much sleep or something, but if this was the case then surely I would wake up earlier? Please help :)