No doubt you would have had this for some time - if not from birth.
My left eye was diagnosed as "lazy eye" when I was a baby and my mum used various methods on me to exercise the eye muscles (like moving toys from side to side in front of my face while dad held my head)

Eye exercises are very important.
Take a look at this link for more information
http://www.strabismus.org/strabismus_cure.html