I don't think I have OSA, and I've always had poor sleep (ongoing), but going on allergy immunotherapy shots has tremendously improved my quality of life.
But I did followup home tests after treating it, and have done polysomnography which is the gold standard of diagnostic test. I also wear continuous spo2 monitoring on a monthly basis to see where I am from my own device bought on amazon
To treat, I needed a team of specialists (sleep doctor, allergist, ent, maxillofacial surgeon, GPs, and a gastroenterologist) to tackle the various causes and measure the effect. I also consulted Dr Kasey Li, probably the world's leading expert on sleep apnea surgery. He recommended his own surgery expanding the maxilla, but I don't think I need to go that far as its very expensive and I am much better today. I've seen several sleep doctors, will list Dr Sinha at peninsula as someone I would recommend, along with AXG Sleep Diagnostics for an affordable polysomngraphy if you need to pay out of pocket. For ENT, I will also recommend Dr Gerald Kangelaris (skilled surgeon) in SF and Dr Andrew Murr (head of ucsf ENT) if you need a second opinion
Also a lot of my interventions are done daily. So if I miss things or get lazy I can recognize if there is a difference. I also motion record myself automatically every night. In the morning I review how much I toss and turn. Its been about a year of experimentation
I have a similar issue where maybe once or twice a night now my sp02 drops below 90, followed by a spike in my heart rate. From the word of my sleep doctor, that is not normal for a younger person. She used this to try to justify the cost of a psg to my insurance company.
Find a different doctor. Young and fat is not the qualifying criterea. From this entire thread you can get a sense that there are a lot of people suffering out there that have sleep apnea but not fat. Also, a take home sleep study is cheap and easy and covered by insurance.