When I read your post I immediately thought of thyroid problems.
It is something that can and does get missed by GPs and they have not been thorough enough with regards to testing.
www.thyroiduk.org.uk/tuk/index.html is a non woo website re thyroid problems.
If they've only done TSH they certainly have not been thorough enough:-
The blood test for thyroid problems is called a Thyroid Function Test. The most usual tests are:
TSH, TT4 AND FT4
There is a range, which is used for the tests. These vary sometimes which is why you must always ask what the range is, so that you can see where you are in the range.
TSH = THYROID STIMULATING HORMONE
This hormone comes from the pituitary to stimulate the thyroid gland into making more hormone. TSH rises when the thyroid is struggling.
The approx. reference range for this test is 0.4 to 4.5.
TT4 = TOTAL T4
Thyroid hormones bound to proteins. TT4 lowers when the thyroid is struggling.
The approx. reference range for this test is 50 to 160.
FT4 = FREE T4
Thyroid hormones not bound to proteins. FT4 lowers when the thyroid is struggling.
The approx. reference range for this test is 10 to 24
FT3 = FREE T3
T4 converts to T3 and is the only thyroid hormone actually used by the body's cells.
The approx. reference range for Free T3 is 4 to 8.3