Nose stud advice - what is the best metal?

I've had my nose piercing for approximately six years, and in the past month it has developed the dreaded bump. Although it is red and there is a very small amount of pus, the bump is not painful at all to clean (I have been using sea salt and tea tree oil for a month which has shown minimal improvement).

I went to the doctor this morning to have it checked out. She agreed that the area LOOKS like it should be very painful, but because it's not, she suspects it's not an infection, rather that my body after six years has started to reject the metal. I don't know what metal it is made from, but I purchased it from a proper piercing shop, so I'd imagine either surgical steel or titanium.

The doctor recommended I get a 24ct pure gold nose stud, insisting this is my best chance of clearing the bump and redness (assuming infection isnt the issue). I am obviously considering this advice, however I've done my own research and have found online that many sites recommend titanium or surgical steel before pure 24ct gold. So, now I'm at a loss and feel like I;m back at square one.

Can any professional piercers clear this up for me? Is 24ct gold a good option, or should I try another stainless steel or titanium stud (the doctor suggested the current one may have broken down a little bit and exposed the piercing site to some of the yucky metal bits).

Any help is appreciated! Thanks!