What is up with me?

I'm 15 and I've had a mild stutter all my life, and when i am talking, i often say the wrong thing; not necessarily bad things but alot of the time i mix my words up, and i have to correct myself alot. I am not very eloquent and i find it hard to articulate things. I don't know if this has anything to do with it, but when i write something, like in my English exam yesterday i wrote a few pages, which i thought i was doing okay with, but when i read it back i had missed off letters on alot of words, for example i spelt "there" like "ther".. this happens quite often. I don't know if there is something up with me, or my brain cells are damaged or something :S or sometimes i think i am ahead of myself in a way, like i should think before i take action.. i do talk really quickly aswell. And also when i read something, I end up staring at the text with no thought process coming out from what i read.. i often have something else going through my mind..whats wrong with me?