I'm actually sobbing whilst reading this thread because its exactly how I feel, the complete exhaustion, confusion, jumbling/slurring words, every part of me aches, not knowing how to explain it to anybody because saying I'm tired sounds pathetic.
I was diagnosed with an under-active thyroid which turns out not to be under-active, the endocrinologist agrees I do have a thyroid problem but in his (and 3 other doctors) opinion it is a symptom of another problem and not the cause.
I was off work for 6 weeks when I could barely get out of bed and returned to work on a reduced level gradually working up to where I am now doing 3 days, even this is to much but I'm a nanny so don't really have the option of reducing less (i should be used to work 4 days).
Everyone keeps telling me I'm looking better but the truth is I've just learnt to hide how I'm really feeling, I broke down yesterday and confessed to my boss that I've fantasised about getting run over just so I can legitimatly stay in bed without feeling guilty 
My GP is really good and has done tests for pretty much everything suggested on this thread and I'm due another round of blood tests tomorrow but when I saw her on Monday she suggested that we need to consider ME and gave me some info to look at.
I know how lucky I am to have a supportive GP and DP and also bosses who have juggled their own jobs around to enable me to drop days (they are both doctors so fortunatly do understand to some degree) but the main problem is me I just can't accept the person I have turned into, I so desperatly want to feel like me again!
OP I only read the first 5 pages but thank you for this thread I really needed to not feel alone in the frustration of complete exhaustion