Tiredness 4 months using CPAP machine. Recommendations?

Hi, I've been using CPAP machine (AirSense 10 Elite) since August 2023. I was diagnosed with severe sleep apnea (AHI 54).

It had great improvements when I first started with a nasal mask. A couple of months later I've started, I notice I was feeling more tired in the mornings again. Dry mouth and waking up several times a night were the symptoms.

I spoke with sleep clinic staff and I was advised to try a full face mask. I tried it for 2 weeks and it didn't go well: majority of the nights I had to remove the mask to allow myself to sleep.

Since last month, I went back to nasal mask but now I tape my mouth. Definitely much more comfortable and I can properly sleep. Although, I still feel tired and with headaches when waking up, even sleeping 8 or 9 hours a night. I've also increase the pressure of my machine from 4-20 to 8-20.

My AHI now based on the reports is 2.0.

I am waiting for a sleep clinic appointment but I was wondering if anyone experienced same kind of scenarios?