I never had an issue with breathing with a mask or respirator. The only issue I ever had was getting sweaty from the heat.
Although it is fashionable, even styleish, to wear mask, many have learned and practice holding the mask just below the nose.
Yesterday at Walmart I observed the widely accepted practice including a mom and two kids with fashionable masks worn with the nostrils exposed for breathing
Perhaps some of that is that you are used to it.
A person who doesn’t normally wear a mask might have more of an issue with it
I run hot. When I start feeling that overwhelming hot flash- not related to menopause but like it- it becomes more difficult to deal with a mask. Psychological component to it as well.