Depression Support Group
Depression is a real and debilitating condition that is often misunderstood by family and friends. Its meaning can range from a prolonged period of sadness to an actual mental illness with specific symptoms. Find and share experiences with others who are going through the same struggles.

Some mild mental illnesses present as other things, in their onset, and so are often misdiagnosed. There should be a long battery of tests to determine for certain.
I agree with bw, get another opinion. And what heretic said. Your inner voice will know best what's really happening.
Maybe encourage husband to keep a short daily journal, with brief descriptions of how he's feeling and what's really going on. That can help with a diagnosis, hugely.
Here's a fairly straightforward answer for you both:
http://www.healthyplace.com/bipolar-disorder/diagnosis/diagnosis-of-bipolar-disorder/menu-id-786/
Hoping you find the answers you seek!
There is also a Bipolar Group here, they might be able to assist you more:
http://www.dailystrength.org/c/Bipolar-Disorder/forum
http://www.dailystrength.org/c/Family-and-Friends-of-Bipolar/support-group
This is for people who have a friend or family member who has been diagnosed with bipolar.
Keep knocking on those doors. It's the only way to find out what's going on.
((More hugs))
That diagnosis was based on my now ex-bf telling her I have a "fiery temper" and me having issues concentrating.... she decided that was me having racing thoughts or whatever...
Anywho, I agree with the others. Get a second opinion.
You don't need to have mania to be diagnosed bipolar II. They are mostly on the depressed side. They don't have episodes of mania. I think it is highly unprofessional to diagnose someone as "slightly" bipolar. Either you are, and have the symptoms in the DSM IV or you do not.
Get a referral to a pdoc, and get a proper diagnosis. It could get worse with time if it is bipolar, and early treatment could help. Or, it could be just a doc over eager to jump on the bipolar bandwagon. Sorry you are going through this.
http://www.sharecare.com/question/bipolar-depression-diagnosed#cmpid=scw
Hope it all helps
http://www.rcpsych.ac.uk/mentalhealthinfo/problems/bipolardisorder/keyfactsbipolardisorder.aspx
I am making a guess that the dr may mean Cyclothymia type? but at the end of the day the the criteria you both need to work on is the impact it has on you.
The book "Loving Someone with Bipolar Disorder" by Julie A. Fast is very good and you can order this from Amazon.
Hope this is of help
PS My ex wife Has Bi-Polar type 1 and daughter type 2