I am 20. my vision in my left eye has been gone since childhood. i have been told it is not the eye itself. also there is no fixing the problem. why?

Amblyopia: Your brain never "learned" how to see out of that eye. Usually the visual system matures around the age of 6 so if you haven't fixed the problem by then you are kind of out of luck. This is why some kids have one eye patched when they're little-- it forces the brain to get the non-seeing eye to learn how to see.

Lazy eye: More than likely, your weak eye is amblyopic or lazy. This occurs for several reasons in childhood. The two eyes may have a muscle imbalance or large difference in nearsightedness or farsightedness. The brain then suppresses one image and the eye becomes "amblyopic". Once you are older than age 8 or 9, there is no treatment as the brain will not alter. See your eye doctor to find out.