Why Can I Not Sleep?

For a few weeks now the most sleep I've gotten is 3 hours. I have tried music, baths, stretching, warm milk, my best friend even tried talking to me for a while, but no luck. It has been affecting me greatly, I have issues paying attention, I doze off for a few minutes without realizing it, when I doze of I mistake reality for dreams. I'm getting worried, I feel tired but I just cannot sleep. My friend thinks it's because I'm stressed but if I am I can't figure out about what. My step mom is a occupational therapist and she says it's because I messed up my sleep time since it's summer, but I've tried everything, I've layed in bed all night with no tv or lights..ugh. I need advice..