RobS, 4 months in Amazon is about enough for anyone,all those books,and gifts going out everyday must be hard work.
As for the fatigue, Anaemia,i suffer from it, its a pain, just kills all your energy,(not physically kills you for a long time), take iron tablets, from the chemist,eat plenty of green veg,apples and other fruit.
Get a blood test,and if youre lucky you want be admitted to hospital for a blood transfusion.
Have a look at your lips, in the corners, small cuts are a sign of Anaemia, as are white fingernails, that stay white after pressing them,also a craveing for certain foods.
Simple blood test will tell the GP,whats up, and its free.
The other tests are not so nice.