Thank you for your kind response.
It's good that you confirm repetitive strain injuries as a cause. Will talk to my GP about Flexeril, it may not be recognised here in England so I might need to look for it's generic source.
You mention Activan; an 86 year old gentleman recently reminded me that years ago a teaspoon of Epson Salts (mangnesium sulphate) was often used for both back ache and constipation.
I have tried it recently and surprize, surprize, it work gently and well to help the constipation but had not much effect on the pain.