whats wrong with my lights?

Unless there is a wiring fault somewhere, yes, you are correct. Since you'll have to remove the right bulb anyway, why not remove the left bulb and put it in the right socket. If the problem goes away, buy a new bulb and put it back in the left socket. If it doesn't go away, then you've at least eliminated (probably) the light itself from the equation.

If it is the bulb, might as well buy two replacements since you have the whole thing apart. Nothing like repeating the exercise again in a couple of weeks, especially since replacements are fairly cheap. Keep the other good bulb in a box on the shelf for those little emergencies (like this one, if you didn't have the cash or time to go buy a replacement).

Might be the bulb. Might be the fuse.