On one side of the porch is a bulb I put in when I installed the fixture about 3 years ago and I haven’t changed it since. On the other side I put a bulb in and its been fine till recently and now I’m changing it all the time.
For a more definitive test, swap the bulbs.
That sounds as if there may be an electrical problem with surges or something. Anyone know more about this than I do? Do you have access to one of those little electrical testers?