Oh dear, Yvonne, you are in danger of "falling down the rabbit hole" into your anxiety again.
For everyone with any health condition, there are good and bad, better and worse days.

Look at what you accomplished last week!
- up out of bed and doing
- stopped messing with the pulse/oximeter all day
- went to the doctor and got a good report
- took a walk outdoors
- had a visit with your son & grandson
- went shopping with your granddaughter, then put everything away

Did you think a week ago that you could have done all of that? Of course you were tired yesterday! And your back hurt from doing stuff you haven't done for a month or more. But then, you "old brain" got in your way! You needed to think "I did a lot after being inactive for quite a while. My body is tired & needs to adjust. I need to get out a book, a glass of water or cup of tea, and relax."

Instead you fell into the old habit - reading "bad stuff" on the internet, getting more and more anxious, using that pulse/ox over and over, worrying...

Today is a new day - will you try using your "new brain" again?
Put away the pulse oximeter. If you are not blue or gasping, just chug along - slow is better than stop.
Focus on CAN DO.
Stop looking for and reading "bad stuff" on the internet. Instead of "over a hundred people had a problem..." think - "wow, millions of people take this drug safely. If I am really worried about it I'll call Tuesday and ask the doctor." (PS My husband took about 3 months to adjust to it, has now taken it safely for years.)
If your back hurts try this little exercise: lie down on the bed, bend your knees, & "hug them" towards your chest. Hold for 10, release, do it again a couple times.

Will you let me know how you are doing today?
Hugs!
Sue