Seeing as you had it pierced with a gun and that there was a "back" to the earring used, I don't think this was a professional piercer to begin with. A professional piercer would have used a needle and a nose stud or nose ring. If I were you, I'd take the piercing out and let it heal completely shut. If you still want a nose piercing after that, I recommend that you find a professional piercer (one that you discuss the piercing procedure with before paying and getting pierced). I also suggest reporting this piercing practice, as it isn't safe.
If you wish to keep this piercing, however, use a saline contact solution to rinse your nose twice a day after using Gold Dial soap to wash it lightly with a q-tip. This will prevent infections and ensure that you're cleaning it well. Turn it when you clean it as well, as that's healthy, too. I have 14 piercings, several of which are body piercings, so I'm well-practiced on the healing process.
It will take a while to heal this piercing. After all, one should be able to change it within 8 to 12 weeks, but that doesn't necessarily mean it's fully healed. Everyone heals differently. Take care of your body first, your body modifications second. If an infection develops, remove the jewelry and see a doctor.
All in all, I say take it out. Wait for it to heal, then see a reputable piercer to re-pierce it. You don't want scar tissue to develop, so play it safe. Do what you feel is right with your body. Good luck.