The patio light next to my garage went out. I decided to replace it along with the two at the front door with new fixtures. The one at the garage still doesn't work. I left this project for another and several months later the two at the front door went out as well. I do have a reccessed light at the front door that is also on the same switch. It's the only one still working. How is that it they are on the same breaker? What could be the problem?

Bugs in the sockets, maybe.