How can I read a book without my own thoughts distracting me?

Up until the age of thirteen I was able to plough through books. For example when I was six I read the entire Series of Unfortunate Events series in two days (non-stop) and when I was eight I read the Harry Potter series in a week. I used to love studying and learning new things, too.

My mum used to have to force me to sleep, so I used to pretend by putting the book under my pillow and then waiting for her to go to bed, so I could read again. In the past few years I have grown to hate reading a studying because as soon as I try I will get random thoughts dominating my head. For example; "which is the best Pokemon?", "Why did Mace Windu take a group of rubbish Jedi with him to defeat the Chancellor?" When I finally finish a chapter or finally finish studying I can't remember what I've read and it frustrates me so much!

I feel like I've lost my hobby and that I've lost who I am. Reading was literally my life and I feel that it's just been thrown out of the window. I've tried eliminating the distractions, but that's a bit hard to do when the distraction is yourself!

I'm an autistic sixteen year-old girl, if that helps?

I hope someone can help me!
Thank you :D