S.T.
I had the same thing happen! I wore cheap earrings (w/nickel) for years with no problem but developed a nickel allergy when I got white gold earrnings. Apparently, white gold is alloyed with nickel :( They were good diamond studs so I had them set in Platinum and I haven't had a problem since. Yellow gold shouldn't be a problem as I don't think they alloy it with nickel (just white gold).