If sight-reading is holding you back musically, here's what I did when I was beginning to learn to play. I would write in the names of the notes above or below the notes themselves, and the fingerings, too, if I wanted. Seeing "G" associated with the G note on the staff, for instance, ground the association into my head such that the black dot on the second line automatically began to simply mean "G" to me. It's sort of like learning another alphabet - just associate the symbols with their letter (or key, or string, or fingering) equivalents. (It's a bit harder for musical notes than for an alphabet, but it works the same way in my head - this image means that thing.)
There are other tricks you could try to increase the associations. For instance, spelling games where you substitute notes for letters help to associate the right name with the right note - spelling words out with notes, playing hangman or Scrabble, that sort of thing.
I also found that diving hardcore into music theory really increased my sight-reading speed, simply because identifying notes, chords, intervals, keys and so on was such a vital part of elementary theory.