My Chess Openings

I normally use Sicilian Defence if I were black, and Queen's Gambit or Ruy Lopez if I am white.

My question is when I use the Ruy Lopez opening, After 3. Bb5, the opponent would normally use 3. ... a6, forcing the Bishop to go to a4. After that, my opponent uses 4. ... b5, again forcing my bishop to go to b3, causing me to have a positional disadvantage. What can I do to prevent or counterattack this? 

I wouldn't say you have a positional disadvantage after Bb3.  Black has opened up his pawn structure, and your bishop is developed.  Just make sure you play a3 or c3 to open up escape routes for the bishop if black advances pawns towards it.

not much you can do to prevent it 5.Bb3 Na5  6.0-0  d6  7.d4
                                                               or6.d4

This is a fairly common Ruy (ECO C70/NIC RL 9.3) used to take White out of his preferred lines but normally leads to a slightly worse position for Black compared to the Main Lines.  On chess.com check out the Game Explorer/Book Openings feature.  http://www.chess.com/opening/eco/C70_Spanish_Game_Morphy_Defense_Caro_Variation