Shortness of Breath (Hard to inhale)

Hi doc. I’m a married 29 y/o male. These last 3 days, I’ve felt shortness of breath. I cant fully inhale (around 70-80% only). I do exhale successfully. Only once every 5-10 minutes I’ll be able to fully inhale. I’ve also noticed, whenever i yawned, I am able to fully inhale (100% success rate). I am non-smoker, I dont eat junk food, drank 1 or none cup of caffeine daily. I’ve got balanced BMI ratio. I do have this ongoing phlegm in my throat (years ago) and mild tiredness. But i dont have any fever,cough,cold or flu. Since working from home during MOC, i usually lay down in prone position while facing laptop. I dont know whether my problem is due to this ergonomic position, the phlegm, caffeine, diet or covid-19. Hopefully you can solve my problem so that i can breathe back normally. Thanks.