It sounds like you are suffering from what is known as "binocular diplopia". I have suffered from the same thing since birth.
It's caused by a problem with the muscles in one of your eyes, which in turn causes your eyes to become misaligned. Normally, the eyes are perfectly aligned and the seperate image from each eye forms a single stereoscopic image. But in our case, they aren't so we see two of everything.
Since I suffered from this as a child (my left eye turned outward), my brain picked a dominant image, and started ignoring the image from the other. Because of this, my left eye is amblyopic, and although it has perfect near and far focus, I still can't see very well with it. It's hard to explain - but it's pretty much like I'm unable to see the small details (patterns, contrast, etc) in an image.
As far as I know, binocular diplopia cannot be treated with glasses. (Though I could be wrong on this) In my case, it required surgery to modify the muscle in my left eye - which I had done at age 12. The result was cosmetic only for me. My eyes appear very straight, but I still see two images. Though since my left eye is ignored, I normally don't notice the double vision. Luckily, the cosmetic benefits have lasted over 13 years so far - but the eyes can eventually become misaligned again.
I would definately recommend seeing your doctor and finding out what your options are.
An eye docotor would be able to tell you more accuratley because there are many things which can cause double vision.