Q: My Son Shows Signs of Bipolar Disorder
Dear Ms. C' --
There is a "test" for adults, that might help if it's "positive" (i.e. says yes he has it) -- but given the age issue would definitely not mean "he doesn't have it" if it's "negative". If his result is "positive", you could take that in and show it to the doctor, as this test is getting pretty widely accepted as a solid tool.
Here's another little essay about the features of "bipolar disorder" as they appear in kids. It tries to distinguish BP from ADHD, but even if your son doesn't have ADHD features, you might still find the tallying up of bipolar symptoms in kids useful, and perhaps this list too could be taken to the doc'.
Just the symptoms you describe suggest that bipolar disorder ought to be considered (i.e. taken seriously as a possibility). Perhaps in your area, with your insurance, you could find a child psychiatrist to see for an opinion? Ask your new husband's doc' for the names of someone solid; or your primary care doc' (or your husband's, if yours is not open to this line of thinking).
And, if you haven't found it already, another good source for you is BPkids.org. I hope someone will help with your concerns soon.