same thing happened to me... it wasn't an infection... just skin discoloration from continuously wearing the same earring in it and not taking it out for a while...it will fade if you leave it empty for about a week.... or just change your earring more often and don't wear the one that caused it for extended periods of time and make sure to wear an earring made of a different metal than the one that caused the discoloration in the first place... even real precious metals can tarnish from too much continuous contact with skin oils... the one that caused mine to do it was platinum.... so it isn't bc your jewelry is fake or anything... hope this helps you and takes away any concern that it is infection.... anytime it is really infected it will get red as hell and sore as hell....
probably an allergic reaction to a type of metal.
Most likely the metal in the earrings were made of somthing cheap. Could be an allergic reaction . Don't fret.