It was when I was about 9. And I spent the night at my aunts house. In the morning I woke to my uncle touching me I didn't want him to know I was awake. He was rubbing me on my legs, I was laying on my side so he couldn't go any further with that. It went on for I don't know how many minutes. But after that I've never spent the night at there house since. And it has stopped for the time being but when ever he was at our house he would grab my butt. It creeped me out so much. And all that has done a lot of damage on me socially, I'm a lot more stand off-ish with people except for my few friends.

How old are you now?

Im 15 now.

What should I do?

You should sit down, with maybe your mom first (that's how I'd do it), and tell her that you need to talk about something important that has been bothering you. Maybe emphasize that you are serious and that you would never make something like this up and that it's important to you that she believes and trusts you.
Then you should ease into the story and explain what happened. How bad you've felt about it since then but you were too scared to talk to anyone about it.
Reason why I personally recommend talking to your mom first is because dads tend to get really angry very quickly. (From my experience) And then you and your mom can talk to your dad together.
Maybe your parents can get you someone to talk to, a professional. Or just talk to you directly.
It's a brave thing you're doing but it's better then keeping it to yourself for a long time.
Secrets like these tend to get heavier with time to bear.

I agree with jondy do speak to your mum,I work at a treatment centre for alcohol and drugs as a support worker and the amount of clients,that come in that have been abused mentally physically and sexually is beyond belief. The more you can talk about it the easier it will feel for you to talk to someone. If you feel you cannot talk to your mum,how about a teacher or a friends mum and I must emphasise TheQuietOne1996 that you are not to blame you have done nothing wrong. I hope this gives you strength,you are so brave to have spoken about this. Take care.