Turn Signals

I have a 1998 Nissan Sentra GXE (1.6). For some strange reason, the left turn signal on my car flashes way too quickly-- to the point that it is annoying. The right turn signal flashes at a normal rate. There are times when the defective turn signal works properly for a few minutes but then it starts blinking at a faster pace. I've noticed that when this happens the lighting is a whole lot dimmer which makes it harder to the signal. I have replaced the bulb a couple of times which works for a while then it starts messing up again. I have checked the fuse inside the car and it looks fine.

What could be wrong with the left turn signal of my Sentra?