nostril piercing

Just received a nostril piercing with 18 ga. nostril screw stud 1 week ago.
No pain, no swelling, no redness, from all appearances it has healed very
quickly.  I've already decided I want to change the jewelry to a ring or
another item, but the people at the shop suggested I wait 4-6 weeks before
changing it.  Is there a particular reason I should wait this long, given
the condition of the piercing?  Also, if I want to go to a larger gauge, do
I need to get re-pierced with a large needle? Thanks for any info...

-john

--
"An intellectual is a man who says a simple thing in a difficult way; an
artist is a man who says a difficult thing in a simple way."

      - Charles Bukowski