I am not a medical professional these are only guesses and ideas on what to try next.

If it was arthritis, you would have a specific spot that suddenly goes bad, in my case the right big toe. But, you describe a whole body problem. So, I think it is a chemical imbalance. Either too much of something or too little of something else.

- Do you take supplements? Should you take something? Do you take something that you should not?
- Are you developing a food alergy - have you been tested for alergies? I worked with someone that described all kinds of wierd problems, he got tested for allergies and found he had a food allergy, but I do not recall what it was.
- I used to work with someone that has celiac disease, what you describe sounds like she was before she cut out gluten, could that be an issue?
- My sister can't eat gluten but it is not celiac disease, maybe gluten intolerance?
- Do you take any prescription meds that occasionally cause a drug or food interaction? Maybe check what you take on web MD to see if there are any symptoms like yours listed under drug interactions or side affects.

If none of the above, I think you need to think along these lines - what are you exposed to that is bad for you?, etc.