How to help oily skin?

In the summer holidays, I'd like to be able to wear no make-up at all for 8 weeks to help my skin clear up. However, my skin is sooo oily, no matter how many times I wash my face, it's still oily. It makes me breakout in blackheads AND spots. I wear moisturizer and foundation 6 days a week too, usually giving my face a break on Sundays because I don't go anywhere. I drink at least 2 litres of water every day, and my skin looks clear whenever I wear foundation, but when I don't, my skin is oily, red and spotty. I'd like to be able to go out and wear no make up at all. What can I do?