Breathing Issues : Help!

Hey guys, I'm 17M and I'm fairly new to mewing. I tried doing it the past week, and I noticed that I can't hold it for longer than a minute, cuz I get a very impulsive need to yawn. I read about it, and noticed in myself too that I don't breathe well from my nose cuz its mostly blocked. What can I do to start breathing from my nose easily?