As someone who has had to deal with mystery symptoms before, here's my advice.
If you take vitamins, supplements, prescription medication, or any sort of daily pill, then stop if possible. Your symptoms might actually be side effects of the medicine or supplements.
Go on an elimination diet for two weeks. If you start feeling better, then assume it's a nutritional or digestive problem and adjust your diet accordingly.
Next, you need to re-consider every single personal care product you use. Soap, deodorant, shampoo, laundry detergent, etc. Avoid fragrances and dyes.
Pay attention to your surroundings when the symptoms happen. Does it happen more frequently after spending a lot of time at home? Does it happen more frequently after spending more time at work? You might be dealing with Sick Building Syndrome.
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Good luck. It took an elimination diet and throwing out all of my personal care products to discover that that I had sensitivity to salicyclates. Nightshade vegetables, a "natural" supplement I was taking, and aloe–all stuff that might be considered "healthy" and under the radar as far as allergies go–give me problems. I'm not saying that is what is causing your particular health issues, but only pointing out how commonplace stuff can fuck your health up and puzzle doctors.