Unfortunately, in some games this does occur, though you made it sound like it's happening in all of yours... Not all games are designed to support SLI or Crossfire, and in the occasional game, enabling them actually hurts performance.
Maybe more specifics on the games you're playing and experiencing this issue with, the resolution(s) being used, as well as your full system specs might allow someone to help you further. Unfortunately, I cannot, as I have rather limited first-hand experience with SLI.