Are the Doctors picking on me?

A few years ago, despite my very good life, I felt tired and depressed. I had no reason to feel depressed at all so I figured it must be a health problem. I went to the doctor and underwent a series of tests, mostly written.
After reviewing the tests, the doctor tells me that I suffer from Severe Acute Depression. I tell him that I am uncomfortable in social settings and he says that I may also have Social Anxiety Disorder.
Now, I felt fine all summer, it was only in the winter that I began feeling rundown and depressed. Upon hearing this the doctor delivers another possible diagnosis of Seasonal Affection Disorder.
So, lets review here what this doctor is telling me, Severe Acute Depression (SAD), Social Anxiety Disorder (SAD), Seasonal Affection Disorder (SAD), are you kidding me? Do the doctors do this on purpose? Why is it that anything that has to do with depression is S.A.D.?
So, I asked a friend why the test I took seemed to ask the same question over and over just worded differently. He said that it was a form of Psychological Inversion Scoring Test. So, basically, the doctor gave me a PIS Test so he could tell me I was SAD.