Can I consider my mouth my third nostril and reach nostril nirvana already?

There's a joke in Russian quite popular among small kids: "The hedgehog learned to breathe through his butthole. One day he sat down to rest and suffocated".

(Hedgehog is the hero if many slightly absurdist jokes).

Hedgehogs can't (to my knowledge), but turtles can! A fact that seeks any opportunity to be shared. (Example source: https://www.livescience.com/61018-turtles-breathe-through-bu...)

You were always there :)

Only waiting to realize.

Let me actually encourage you try this. Imagine you have a third nostril placed between the 2 real (forming a line or a triangle - whatever you like better), visualize and "sensualize" (do your best imagining it in details and feeling it) breathing through 3 nostrils. As a result this may trigger a nasal congestion relief. Try this the next time you catch a cold.