Re: brain fog
I often experience a type of "brain fog" with allergies. Have you tried changing your diet? That could possibly be the culprit if it is an allergy since you have already tried changing environmental factors.
Brain fog is commonly experienced with Fibromyalgia and Chronic Fatigue patients as well. However, it could just be linked to your previous drug use. Do you have any other symptoms that are common with allergies (runny nose, sneezing, itchy skin or eyes)? If not, it may be difficult to find the source or even to convince an allergist to test. Have you done any research on potential long-term effects of using meth?
One last thing to check would be to find someone who looks at all hormonal and/or nutritional deficiencies you may have. Your homeopathic doctor may be able to help with that. Many of the tests a general doctor will run (such as iron, thyroid, etc.) will show up more or less normal, but they don't always run the more detailed tests (for example, you want to ask for a free T-3, free T-4 and reverse thyroid test rather than just having a general test run). Sometimes the results will appear normal with a general test, but with more detailed testing, major issues may be observed.
Sorry I can't be much help except to say that, yes, sometimes it is associated with allergies, but I would think there would be other symptoms as well. Good luck - I hope you can find the cause and treat it.