Hi.
Thanks for your query.
Noted the history about a 61 year old female otherwise in a good health and understood the concerns.
Kayaking can definitely cause pain in the low back due to muscle spasms or enhanced
osteoarthritis like sacroiilitis or intervertebral join inflammations.
The upset stomach can be due to an intestinal infection that can be detected by tests of stool and blood. If these are normal then this may be
stomach flu too or intolerance to certain foods or beverages.
Hence I would advise you the following:
Take probiotics, activated
charcoal tablets, yogurt and bananas.
Take an antibiotic if there is any evidence of an intestinal infection.
Take plenty of oral fluids, fresh homemade foods, boiled and cooled water.
No outside food please.
Take rest and further management as will be decided after clinical evaluation and correlation with the reports of investigations.