Is there any change when you turn on the lights?
The first and easiest thing to do is to change out the lightbulb. This is probably not the problem, but it's a quick check. You could even switch bulbs between the sides.
My guess however is that there is a problem with your multifunction switch. (Left side of steering column, the thing you actuate to turn the blinkers on) It' not a difficult replacement, but I would eliminate other things first. The part is around $80 ish, I think.