Interestingly enough, I'm now thinking twice about the iron tablets.
Following up on a couple of comments people made, I decided to do a bit more reading.
Liquid iron supplements can stain the teeth, but not tablets, so that wasn't an issue.
However, the interesting question is the causes of iron deficiency.
I eat a diet with a reasonable amount of beans, green veg (veg box and allotment), brown rice and a small amount of red meat, so should have enough. Therefore, it was either the pain from the pulled chest muscles that was causing the tiredness, or, if I am actually anemic, there is probably an underlying cause.
In people over 60 (and I'm on the good side of that by fewer years than I'd like...) one of the potential causes of anemia (once you rule out several that are unlikely to be me) is bowel cancer.
My mother-in-law died of bowel cancer that was diagnosed too late. She was diagnosed as anemic and put on iron tablets for a couple of years, but it's clear from the NHS website
that she should have been tested for bowel cancer at that time.
I would be extremely angry about this, except for the fact that she had gone blind. Her quality of life had dropped dramatically and she was bored to tears. She had an active mind and was no longer able to read the book she loved, do her cryptic crossword or even garden reliably. I nearly cried when I realised she'd planted half her cyclamen upsidedown. Her garden was her life. The cancer gave her an escape from a life she no longer wanted.
(brief pause while I cry. It's eleven months since Molly died and I still miss her. I have many of her plants growing in my garden and I tend them with loving care)
Back again. To cut a long story short. I should stop taking the tablets and if I find I'm getting tired again, I should visit the doctor and get a blood test to see if I'm actually anemic, and if I'm actually anemic, whether there is an underlying cause.
So, let's do this scientifically.
I'm going to stop the tablets today and see if I continue to improve.