You might need to see a different ENT (Ear, Nose, and Throat) doctor since maybe the doctor you saw before missed something. It is important to see a specialist (not just a primary care doctor) and it is good to get a second opinion. You might have a deviated septum or something similar :
https://www.mayoclinic.org/diseases-con ... c-20351710 and you might need surgery, although that might not be doable until after the pandemic.
In the meantime, while waiting to see a different ENT, I agree with the other advice. Try a flat pillow, a cervical collar, and Flonase nasal spray ( if your doctor agrees about the Flonase). I use no pillow at all, but due to a back condition, I sleep flat on my back all night. No pillow works for back sleeping, but might not work for side or stomach sleepers.
If you and your family have enough money to spare, maybe try buying a Bi-level (BiPap) machine because the exhale pressure is reduced. For me, it helped with my aerophagia. I suggest the ResMed AirCurve 10 VAuto. I have the Philips Respironics Dreamstation BiPap and I don't like it because the water chamber is too small, half the time it wakes me up with a burning smell when the water runs out.
I need a minimum pressure of 12.5 cm to help my apnea, I would do poorly if I used a minimum of 10.5, but everyone is very different.
Keep trying different pressures, and try straight CPAP versus APAP. If a straight pressure of 10 didn't work, maybe a constant pressure of 12 would.
I agree with everyone that it is important to try wearing a cervical collar. If I forget to wear my cervical collar, my AHI is about 15 or 18 (even though I'm using CPAP), whereas it my AHI between 0.5 to 2.2 if I wear it. I tried so many different styles of chin straps but they didn't help, my jaw was still able to drop I guess. The cervical collar really helps. I like this one:
https://smile.amazon.com/Velpeau-Brace- ... B072Q93K6Y . But you have to experiment with different height collars, because some people need height 3", some 3.5", some 4". If you get the wrong height collar, it either won't work or it will be uncomfortable. So you might need to buy a few to see what works. You need a flat pillow for this to work. Your neck should be as straight as possible when sleeping. Don't let your head hang back either, I don't think you need to stretch your chest.
Also, if you are wearing a nasal mask, try a full face mask. During sleep, I become a mouth breather and that defeats CPAP, so I need to wear a full face mask. I love my Resmed Airfit F20 full face mask (even though I look dorky like a fighter pilot). I know all this costs $$$ but you are still having terrible apnea, and you need to spend whatever it costs to resolve that problem.
You say there is martial law preventing you from buying a cervical collar. Is it possible to mail order one? Do they have eBay or something like it in your country?
I really hope you are able to be looked at by a nose specialist to look for structural problem such as a deviated septum. You are relatively young to have apnea. Plenty of thin people have apnea though. I was skinny and underweight (female) when diagnosed and my sleep specialist took one look at me at our first meeting and said, "You don't have sleep apnea". But I had the sleep study done and had an AHI of 24 so he had to eat his words. But since your nose is always stuffed up, that is the problem that needs to be solved. If you need nasal surgery and have it done, you may not need a CPAP anymore. I've heard many people say they had some sort of throat surgery for apnea and it didn't help, so I'm skeptical of those types of operations. It is possible that allergies are blocking your sinuses and it is not easy to determine what is the thing you are allergic to. But first, check for a nasal structural problem, it might be that simple.
