For thyroid - a blood test :
The above test package includes a reverse T3 test. A cheaper test package is available without the reverse T3 test included.
For adrenals - a saliva test :
For the above tests you need to order the tests, then the kit required and all the necessary instructions and packaging are sent to you. Payment is requested when you return the samples, not before.
A good blood test which includes full blood count, liver and kidney function tests, and several mineral and vitamin levels is :
privatebloodtests.co.uk/ Then click on Comprehensive Plus V Blood Test (on special offer just now) at the top of the column on the right hand side. The B12 test included in this package is not the best or most accurate type. For that you need the Active B12 Test, also offered by the same site, or get it from elsewhere. The tests from this site require attendance at a Spire Hospital to get the blood taken.
Are you taking any supplements? It is a good idea to stop supplementing some things before testing e.g. iron, B vitamins - how long you need to stop for depends on the supplement and the test being done.
With any testing there is always the possibility that everything could come back normal and you end up no further forward. It's a gamble.
Please bear in mind that your doctor might do some of these tests which would save you money (although they won't do the adrenal saliva testing, and thyroid testing is usually just TSH and - occasionally - Free T4).