is there something wrong with me?

Stress can effect your sleep and thus make you feel tired all the time, as can anaemia and a bad diet. did your Dr take your blood for analysis? skipping your classes and not doing your work is only going to make you feel MORE stressed and unable to keep up with the rest of the class. if you are skipping classes what are you doing during that time? do you skip the class with anyone else? is it the same classes you keep skipping or is it more random? what is it that makes you decide not to attend? what are the thoughts that make you not go? do you decide its too boring? or that not going won't matter or make much difference? you need to challenge the specific thoughts. you also need to start telling yourself that you don't have to act on your thoughts or feelings. you might feel like not going and skipping the class, but that does't mean you should act on that or do anything about it. adults have to do all sorts of things they don't really WANT to do, but they have to be done,so you just get on with it.

Laziness is a normal adolescent thing, and it doesn't reflect bad behavior or health. Try harder, hun. :)

It's a faze your going through.