Oh, my dear, my heart goes out to you and your DS.
We've had similar, in that my 15 month old DS has been rushed (blue lighted) to hospital 3 times in 4 months, really struggling to breathe. It's not been Covid yet, but different, usually mild viruses.
Last time, he was gasping at 124 breaths a minute (should be 40 a min), and his oxygen levels were 69%. He goes downhill so quickly.
However, a couple of days on oxygen, steroids and sometimes antibiotics, and he's back be being the little terror we know and love.
If the hospital is concerned about him having Covid, they can run a Nudge test, which will give a PCR accurate Covid test within about an hour. The kit for these were released to hospitals in the first few days of September.
It's terrifying when they can't breathe properly. DS may be rushed to Resus, but this is just because they have the correct kit to help him there.
My prayers will be with you both. If there is anything that you don't understand, or are worried about, make sure you ask.