You might not ever know what caused full blown bipolar. I've had bipolar symptoms since I was a child. I don't think most of us can pin point an exact cause.

I hope the journaling helps you figure stuff out. With myself I know there is no thought that triggers my mood shifts, I'm talking about acute episodes, not just normal moods tho. I'm not sure if that's what you are talking about? When I have either a depressive mood shift or a manic shift it's usually a combination of things.

I wish you luck with this, hope it helps.