Hi....I am going through the same exact thing with my 14 year old daughter....they cannot definitively diagnose her and are treating her as if she has a mood disorder and the traits that they see. I have been told that with kids, even in adolescence, they cannot clearly diagnose any particular disporder until around the age of 18. As a mom that is quite difficult to understand because we have that need to know what is going on so we can know that we are doing the right thing.
I was told that bipolar is considered to be a mood disorder or an affective disorder. Like Becky already said, there are many disorders that fit under these categories and depending upon what traits are demonstrated at a particular time they are treated as so.
With my daughter, I have been told that they are treating it as if it were a "mild bipolar II" without diagnosing it as so but having similar traits of depression and manic tendencies that is how they determined which meds would be best to start her on. I have been told that she will be monitored and most likely off the meds in about 6-8 months but that still has yet to be determined. From some of what I have read here, for the most part when you are clearly diagnosed with a true Bipolar you MUST be on meds. But then some are either misdiagnosed or only possess the traits of the disorder and treated accordingly as is the case with my daughter. So I guess that with both of us time will tell....you having more time than me!!
Since I am only new to this myself I can only share with you what I am going through. I do know as a mom all we want is to know that are kids are happy & healthy and so long as that is our driving force then everything should be okay.
I wish you luck with you son.
(((HUGS))) ~ Goody