How do you tell the difference between normal mood fluctuations, the bipolar part of mood changes, and mood changes that relate to experience/trauma?

I thought I could tell but lately I have no idea anymore why things change the way they do. I feel less able to control the shifts or understand them.

I used to be able to "control" things by saying, "Oh it's just the bipolar screwing with my moods/emotions" but that doesn't seem to work anymore.

I've been very stable for about 6 months - the most stable in about 4 years since my original diagnosis (bipolar 2).

Thoughts?