Your doctor is right about this. If you track your mood you can see if your mood is independent of the external events that are happening in your life. Like for instance, when I become hypomanic I have a tendency to feel intense emotions for a person and dream of affairs. I also sleep less and feel better about myself independent to what is going on. I get triggered easily and my happiness can easily turn into anger. It hurts my grades because I care less about how I am doing and I get obsessed with something else. Everyones experience is slightly different depending on severity. There should be some kind of pattern though

External events do cause a person to react negatively or positively. As patients we need to learn to distinguish normal reactions fron bp reactions and only time and perseverance to see those patterns will help. (You can use various things to do this)