Porch light problem?

Don't know how old your fixture is. If it has some age to it, another thing to check might be the socket itself. After numerous bulb changes the tab inside the socket might be compressed so much that you may naot be getting a good contact with the bulb base. With the power off use something non metal to pull the tab upward a little. That may solve your problem, if not then you will have to check to see if you are getting power to the socket itself. If no power there are you getting power to the switch? If not, check circuit breaker to see if it has tripped. If not then you have an issue that will probably need a qualified electrician.