What is the best move here?

This is from one of the games in which I lost! :( This game can be entitled an upset as my opponent was -200 from me. Well, now as to the question. What is the best move here? And what was your thinking process when you came up with this move? 

One more question: If I cannot find any tactic, what should I do? 

I recommend 5...Nc6

a6 b6 Nb6 something on that side of the board to help open things up. These kinda cluttered positions are pure death when your opponents clutter is more deadly than your own. Your clutter is doing absolutely ZERO while your opponents is barreling down on every side. You cant contest the middle, or kingside, so you have to initiate something on the queenside and do so quickly.

I recommend nc5