Unplug the bulbs and switch them side to side, then see if the same bulb acts up. Hopefully just the bulb will be burning out. They are only about 100 bucks. If the left side still has the problem, suspect the ballast. They are much more expensive than the bulbs.
Don't touch the glass part of the bulbs. The oil from your fingerprints will burn through the glass.
The fuses and wiring aren't the problem. When fuses blow, they don't start working again.