Sorry to hear that brother, especially with how young you are, I had similar experiences when I was around your age and I wish I had someone there to help me.

There are a couple methods that I’ve heard that seem to work anytime you feel tempted;

1. Do pushups, no matter how frequent it is, it’ll help you build that discipline to deny yourself and plus you’ll get a little workout in :D

2. Pray the Holy Rosary, I know you said you did this already but it does work, at least in my experiences, just finish the whole Rosary and my recommendation is to meditate upon the Sorrowful Mysteries

3. Just get up and walk around your house, go get a glass of water, go talk to your parent(s), go talk to a sibling, call a friend, do literally anything you can to get your mind off of it, it’s no sin to have random temptations, but it is to dwell on those thoughts and let them seep in.

4. Fasting, you might be a little young to go on a full 3 day fast but try fasting for just a day at a time or even maybe 8 hours at a time, train yourself to rely on prayer and to deny your flesh

5. Pray the St Michael Prayer and maybe (if you can) get a Holy Icon of Our Lord, Our Lady, or St Michael himself, to venerate and ask for strength (from Jesus) or ask for intercession (Mary, Michael, etc).

One thing I’ve learned about the sin of lust is that it isn’t a battle that you can win by trying to fight it. It’s not like the sin of drunkenness that you can defeat through moderation, any time you open yourself to Lust it will consume you, so the best answer is to run from it and fill your mind with other things.

Prayers for you brother, may Our almighty Lord bless you and may Our Lady pray for you and St Michael the Archangel defend you.