Greasy Hair

I've had greasy hair since puberty (those were rough times...) it's always right by my scalp and it makes it look like my hair is two different colors because the greasy part is darker. It's ok for a few hours after I wash it, but any longer than that and it's just embarrassing. Does anyone have tips for this? I use Head and Shoulders shampoo and Aussie conditioner. I tried to 'train' my hair (gradually wash it less frequently) but it's still embarrassing. I'm at college all day, so I don't have the opportunity to wash it 3 times a day