Wow---this has been going on for 7 years?! It is good news that there has not been anything significant in the test results (ruled out the worst-case conditions it sounds like), but no less frustrating that you want to know what is going on.
Did you see the previous post regarding "thyroid hormone and insulin levels could contribute" ? You mentioned that you had blood tests, and I'm wondering if these have also been checked? Have you had a second opinion from another doctor?