For A While Now Ive Had The Feeling That I

for a while now ive had the feeling that i cant take a full breath of air. i seem to get a full breath when i yawn or if i lay on my side in bed, or even do the 478 breathing method. I smoke marijuana and i never had issue but at one point i picked up a nicotine vape from the local 7/11. After that is when i started to get the shortness of breath. i just want to know what can be causing it or how i can help reverse it because it makes me scared and i almost want to panic but i try to stay calm to slow my breathing down.