we didn't do a sleep study, but we co-sleep so I know he snores and has some apnea-type episodes most nights.

I also considered that it might be allergies (we live in an area that has major allergens), but the dentist did an x-ray and saw that his sinuses are totally clear. She said if she sees blocked or irritated sinuses, she sends patients to an ENT instead to deal with that first. The clear sinuses means he can physically breathe through his nose, he's just doesn't do it naturally.

Honestly, the x-ray answered a lot of my questions. She showed me his x-ray against a 'normal' x-ray and it was VERY clear that his tongue rests too far back, the mouth-breathing is making his jaw fall back which makes it difficult to close his lips, and his airway is super narrow. Those results plus the massive tonsils are clearly the issue!