There is a false dichotomy between "endogenous" and "situational" factors causing mental illness. Yes, MI (and especially bipolar) is biological. But psychological factors and life situations heavily influence mental illness.

Prior to my first depression when I was 12, my best friend abandoned me and I had surgery. I believe that these life experiences contributed to (and possibly even triggered) my illness. That doesn't make it any less biological.

Just because you can think of environmental triggers for most of your symptoms doesn't mean that they are purely "situational". There is an interaction between nature and nurture. Psychologists call it the "diathesis-stress" model; environmental stress and biological diathesis work together to shape behavior.

I can't answer your question as to whether or not you "really" are bipolar. I can tell you that if treatment for bipolar has helped make your life more tolerable, then you ought to continue it, regardless of how you identify.