What Causes Blood Blisters In Ear After Getting It Pierced?

My 5 year old daughter had her ears pierced by her Pediatrician about 4 months ago. We have kept her ears clean & she wears 14K gold studs. Yesterday her left earring hold began to bleed. When I took the earring out there was a small black blood blister. I cleaned her ear & earrings with alcohol & put them back in. I cleaned her ears again this morning. Tonight she still has the original blister and her right ear has a developed a blood blister. I'm not aware of any trauma & she said that she has not hit it. I cleaned her ears & earrings again w/ alcohol & put Neosporin on them. What could be the cause of these blisters? Is it safe to wait a couple more days before taking her to the Pediatrician? She is very healthy & active. The only issue she has ever had is eczema.