Has what you described been your baseline mood/tendencies throughout your life? If so, I'd address that with your psychiatrist and therapist. If not, then something obviously changed for some reason. Identifying the reason can help you work to change or accept it.

I have has some periods when I was as you describe, but my baseline is actually quite hyperthymic. For me, depression, dealing with some trauma, and/or working through periods of social anxiety were likely the cause.