It looks like either a granuloma or follicular cyst, which are both incredibly common with nostril piercings. You don't need to remove the jewelry in most cases. For starters, no more playing with your jewelry. I understand you did for photographing purposes this time, but be mindful about movement of the jewelry as that is what usually causes a these types of bumps.
If you were started with a longer screw to accommodate swelling, first things first, go back to your piercer and see if it's time to change it to a shorter screw that won't wiggle and slide back and forth so freely. Jewelry that sits crooked or slides around puts uneven pressure on the fistula (healing tunnel of scar tissue inside the hole) which can cause these little flare ups.
If you already have in standard length jewelry you can apply hot saline (same method as sea salt soaks) or chamomile tea compresses to the bump for ten minutes twice a day. Don't fiddle with the jewelry. Don't push on it, rotate it or try to change it yourself. Don't use products not meant for piercing aftercare such as ear cleaning solution, Bactine, rubbing alcohol, peroxide, iodine, witch hazel or antibiotic ointment.
If the bump does not reduce in size within a week, go back to your piercer and see what they recommend. If it puts your mind it ease, it does not look like a keloid. It looks like a normal nostril piercing bump. Unsightly and annoying? Yes. Dangerous, untreatable or a sign the jewelry should be removed? No.
ETA: Since I just saw the whole, "it's an allergic reaction so use sterling silver" comment and I felt a duty to address that. Not to call anyone out, but to bring it to the asker's attention. Sterling silver jewelry is never, ever suitable for a healing piercing. I'm certain the screw is surgical steel. If it is a metal reaction it's rare, but not unheard of, with surgical steel and a switch to titanium jewelry would solve the problem.
Sterling silver oxidizes inside a wound and leaves a permanent black mark on the surface.