My ears always get infected when I wear earrings. Usually they hurt within a couple hours of wearing them. They're less sensitive to real metals, but they still usually end up infected. I was browsing the cheap earrings at a store a couple of weeks ago and asked the girl there if she knew any tricks for people who are sensitive to cheap crap. She told me to coat the parts of the earring and the backs that touch your ear with clear polish. Sounded iffy but I tried it and it works! I've been wearing five dollar earrings with no issues for over a week now.
PS. Don't forget to coat the part that pokes through your earring hole.