Quick ear update. Apparently the lump was scar tissue - there's a condition where the body just keeps producing it and you get weird lumps, usually on the shoulders and back (hypertrophic scarring i think it's called). I've got another one on my shoulder from several years back. So basically my ear kept trying to heal itself, but with the earring in it couldn't.
I went to a plastic surgeon who sliced the lump off the back of the ear, and the little one on the front, and cleared out the scar tissue in there too. It was.. an experience :) But it's done now, and hopefully with the earring out, the scar should behave itself and just heal normally.
So in summary, i don't think it was caused by infection, I did try to keep it clean. On the other hand, if i had picked up on it early and removed the earring, it probably wouldn't have needed treatment.