How could i be allergic to silver but not cheap metals or metals with other impurities?

for the last 10 years I have been wearing cheap jewelry from dollar stores, walmart and street sellers etc basically I've never had a problem with any type of metal earrings but my husband just bought me real silver earrings and I seem to be allergic. my ears swell and the backs get crusty and hurt. Theyre stamped as real silver but even still I dont think its a problem with impurities since I have not had any trouble before. I wear silver necklaces/bracelets all the time against my skin and ive never had a problem. Im also positive that ive had silver earrings stamped 925 before but ive never had this type of reaction. what is it and is there anything i can do?