How do doctors diagnose fibromyalgia?
BMJ Group Medical Reference
It can take a while for a doctor to diagnose fibromyalgia.
Because pain and tiredness are so common, your doctor may think your condition has other causes, such as the flu, or an illness like depression. People with fibromyalgia often have other conditions as well, which can complicate the diagnosis.
There’s no laboratory test that can tell if you have fibromyalgia. But doctors use guidelines to diagnose the condition. Here are some things your doctor might do to work out if you have fibromyalgia. 
Questions your doctor might ask
Where on your body do you feel pain? (People with fibromyalgia have pain around their body, not just in one place.)
How long have you had this pain? (Pain is described as long-term if you’ve had it for three months or more.)
How do you sleep? (People with fibromyalgia often have disrupted sleep and feel unrefreshed during the day.)
What other symptoms do you have? (People with fibromyalgia often have other conditions, and your doctor will want to know if there is anything else associated with your condition.)
Your doctor will want to know how your condition is affecting your life. He or she may ask you questions from a questionnaire that’s designed to find out how you’ve been in the past week.  The questionnaire is called the Fibromyalgia Impact Questionnaire. You can see the questions on this website: http://www.myalgia.com/FIQ/fiq.pdf. This questionnaire is often used in studies of treatments, to see whether the treatments help.
Your doctor may ask you to undress, and he or she may press certain points on your body to see if they’re painful. People with fibromyalgia often have pain at certain points, where other people don’t feel pain. If you have pain at 11 or more of these points, then you probably have fibromyalgia. 
You won’t need other tests for fibromyalgia. But your doctor may do some blood tests, to check for other illnesses that might cause your symptoms.
If you have blood tests, your doctor might check for signs of inflammation that could be causing your pain, for anaemia, and for levels of thyroid hormone. Anaemia is a disorder that can also make you feel tired and that is often caused by a lack of iron in your diet. Your thyroid is a gland in the neck that helps regulate energy levels. If the hormones it produces are too low, you can feel tired. The tests are likely to come back normal. But even if you do have another disorder, you may still have fibromyalgia. Some people have fibromyalgia as well as another illness that causes pain, such as rheumatoid arthritis.