Hello @dersh, I would like to add my welcome to Connect along with @kittykelly1234 and others. I've had a similar experience with my CPAP when I had been using it for awhile which started me on a quest of trying many different full face masks. I'm currently using the ResMed AirFit F20 full face mask but still looking and may switch back to one that fits under and up against the nose that also covers the mouth. I've always been a mouth breath myself which I think is partly because I have a deviated septum.

I met with a Mayo ENT a year or so ago to discuss my options. I didn't really want surgery and was happy when he put me on a proprietary nasal spray plus having me do a saline nasal rinse twice daily prior to using the spray. This made a world of difference in my ability to breath through my nose on both sides. Prior to that my right nostril was always plugged up and sometimes the left one was too. I used the nasal spray for 3 months and then just stayed with doing a nasal rinse in the morning and evening every day which has worked pretty well most of the time. I also found that if I take a menthol cough drop a little before I go to bed it opens my nostrils and lets me breath better at night.

Last month I ran across a device call SinuSonic (https://sinusonic.com/) which intrigued me a little. I read the study referenced by the company and decided to try it. I've been using it twice daily instead of the nasal rinse and find that it has helped considerably with my stuffy nose. The device lasts for 6 months before you need to replace it so I thought it's similar in price to my nasal rinse product and much easier to use. Here's a link to the study:
-- Correlation of Exhaled Nasal Nitric Oxide With Sinus Computed Tomography and Sinonasal Outcome Test Scores: A Cross-sectional Pilot Study:
https://www.researchgate.net/publication/327813408_Correlation_of_Exhaled_Nasal_Nitric_Oxide_With_Sinus_Computed_Tomography_and_Sinonasal_Outcome_Test_Scores_A_Cross-sectional_Pilot_Study
Please don't give up on the CPAP, it does normally take a minimum of a year to get used to it. I was fortunate that I had a local medical supply company with a sleep therapist that helped me with all of the mask issues.
Have you discussed your problem with the CPAP with your sleep medicine doctor or care team?