Why is my oxygen dropping? 3rd hospital visit in the last year.

36 Male 6"1 260lbs. Asthma, Low iron. Just got my first ever iron infusion yesterday. Currently in the ER after waking from a nap and coughed up a little yellow pleghm. Oxygen @ 90%

I had 2 previous infections of pnemonia in the last 12 months.

Never had i had anything like this in my life. Ive been hospitalized for upper respiratory infections but this is getting excessive.