headshrinker,
There’s a Yahoo group "hypogonadism2" that deals with all of this in great detail.
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You would want to test Total and Free Testosterone, and Estradiol, which is the main form of estrogen that has effects in men (don’t test for Total Estrogens, which is meaningless in men). These are simple blood tests.
Of course being a UK person, you may have trouble convincing your doctor to order these tests. You would have the same problem in the US, but would have the alternative of ordering the tests online (lef.org and similar sites).
If Estradiol is too high, you would want to treat that first since doing so will raise T levels without using any T supplementation. However, finding a doctor who knows anything about estrogens in men, and is even willing to test them, is difficult. Go to the Yahoo group and ask about all this. There may be others in your area who have faced the same problems.
By the way, the "symptoms" you describe don’t necessarily mean your testosterone is low. So don’t be surprised if the tests come back normal.