Bring up PP Depression?

I am 4 months PP & have an appointment next week with my OBGYN. For a few months I've been feeling bored, anxious, emotional, unhappy and just always feeling "so-so" in every aspect of my life. I'd call my life mediocre at best. My friend is even having a birthday party this weekend that I already do not want to go to. I'd honestly rather just be at home.
This may be a silly question... but is it too late to being up PPD with my doctor since its been 4 months? How do I even bring up a subject like this? What if my doctor just brushes it off and says "it's just your hormones balancing. You'll be fine?"