I have a bump that grows and shrinks but never goes away. plz helpp?

so... maybe like 3 years ago i pierced one of my ears myself but it was with a used earring but i cleaned it reallyyyy good. i only left it in for about 2 days cuz it was feeling really puffy, uncomfortable. so i took it out. ever since then ive had this huge bump there and sometimes it gets really big and itchy for no reason and other times it gets smaller and doesnt itch but never completely goes away. when it gets big it gets hard but when it shrinks it softens up. my dermatologist said he thinks its just some kind of cyst and that it isnt dangerous or anything but im just not really sure. i have other piercings and nothing like this has ever happened to them and i pierced my other ear myself and nothing happened to it. i might just be paranoid but im just worried it could be somethimg serious like cancer or something. i realize it was dumb in the first place in case anyone wanted to comment on that. plz help thanks so much :)