Here is my code.
http://pastebin.com/ViGnsBKb
Every other side is fine except the left side, every time the character got collided on the left side, it will get stuck, and not move anymore, until the character jump to uncollide with the left side, then, the character is released. I think it is having something to do with resetting the x velocity.
This code works before, one day I did not know what happened and the right side started to react like this. Trying to fix the right side, trying multiple things. One day it randomly worked again. But the right side started behaving like the right side. I really do not know what is going on.

