Why do I mix up words and letters in my head?

Alot of times when i see, hear, or say a word, in my head ill mix up the letters to see what it sounds like or looks like. I can also read backwards, almost fluently. Also, the letter mixing up has almost become an obsession. It doesn't bother me much. I was just wondering what it meant. I'm a 14 year old male with an IQ of somewhwere in the 120's, just in case that might help.