Beth's suggestion of a mood tracker is excellent.
I initially kept a journal for months, and felt that a mood chart wasn't able to adequately describe what I was experiencing.
My psychiatrist asked me to diligently fill out a mood chart every day, and the results were alarming to say the least.
At a glance he was able to see how my moods reacted to medication changes, and how long my cycles were lasting, or how mixed they were. It gave us a quick handle on the issues and we were able to spend the rest of each session refining our plan of action to tackle the disorder.

I still keep a daily journal and it provides useful qualitative information when I want to provide my pdoc with the details (evidence) of what I did during a manic state, or how I avoided suicide during a deep low, etc.