You are struggling with the sin of masturbation? The best advice I can offer is that you can’t do this alone.
No matter how hard you think about it, how often you go to confession, pray about it, or feel ashamed about it–all of which are absolutely good things–you really need to engage this by finding something good that you are more passionate about doing than experiencing the transient pleasure associated with masturbation.
Instead of always thinking about the sin and either about how to avoid it or how to engage in it, I strongly urge you to get involved with a group, take leadership roles, assume responsibility for something greater than yourself. One of the biggest obstacles, I think, to people stuck in this sin is a lack of discipline. Get involved with something that FORCES you to do something outside of your room. Get involved with something that makes you feel good about yourself and what you are offering to the world.
I often thought that this sin could be conquered just by praying, reflecting, or feeling REALLY REALLY bad about myself. That’s a bunch of … well, you know. Do something and just keep doing it.
You really need to go to Confession tomorrow. You know that you sinned. Confess it and ask for a more difficult penance than “pray a rosary.” You can do that, you know. Ask the priest if he might assign you a more difficult penance that will make you feel the pain you caused our Lord and Savior Jesus Christ. It may help to overcome the lack of discipline those caught in this sin have.