I bet it's a nickel allergy. Have you noticed any symptoms beyond just the issues with your earlobes? As in, do you have itching on the sides of your fingers or the bottoms of your feet? Do you have any reactions to nickel coming into any other contact with your skin, e. g. the zipper on a pair of blue jeans?
I'm sorry for the pictures in this url -- so scroll quickly to the bottom and you won't see 'em.
http://dermnetnz.org/dermatitis/nickel-allergy.html
If you scroll up a little bit, you'll see a diet you can follow which can help to alleviate symptoms.
I hope you feel better soon.