I definitely beleive that stress, illness, or pain can all cause upsets in glucose levels. I've certainly seen fluctuations and slightly higher levels in mine if any of them are affecting me!
It's maybe worth keeping a readings and health type diary to see if you can see a relationship?
There's differences of opinion about the efficacy of taking glucosamine/chondroitin to relieve joint pain but I can certainly feel the difference in my knees if I stop taking it, so maybe that 's another option that may help.
Robbity