Just print out this
American Family Physician's article
this PMDD DVM-IV article
with the chart filled out. If your doctor isn't familiar with PMDD then give him/her these articles. It's up the individual doctor to keep up with the latest research on the subject. Sometimes their interests lie elsewhere or they've made up their mind long ago that PMS or PMDD isn't worth their time to treat.
In most cases you'll receive a referral to an OBGYN who will know more about the condition but unfortunately they have only two recommendations at this time- the pill or an antidepressant. Currently most of the research regarding SSRI's and PMDD has been funded by pharmaceutical companies. Now don't get me wrong, SSRI's have helped many women make it through very trying circumstances, but remember they are only a band-aid to an underlying problem. Understanding the cause of your PMDD or extreme PMS is the only true answer.
It's up to you to try and understand your body's symptoms. There are many reasons why PMS/PMDD surfaces in a woman's life-- malabsportion, a bad diet, stress, underlying disease or illness. If the doctor can't find anything wrong with you then chances are it's related to nutritional and stress factors.
Please read through the website and learn as much as you can. You have to insist that you be tested for nutrient deficiencies because they won't order these tests on their own.