I know people aren't snakes and snakes aren't people.
But a upper respiratory infection is pretty similar in most animal species, incl. humans.
They never just go away in a week or two. Drainage continues for a good while. And a snake doesn't have nose spray and tissues. I would think it would be pretty normal to have dried mucus plugging up the nostrils and make breathing a bit harder at times. Esp. if it only happens occasionally now and isn't constant or getting worse.
I think overall things are progressing quite positive. Just hang in there..