Depression has no reason

I have depression. It's not because there is something wrong with my life. It's because of chemicals in my brain. This should be clear to me especially now. I was having horrible intrusive thoughts today and yesterday. Just overall very symptomatic. Why? I have an awesome boyfriend. I have a job that pays me more than I've ever made before, that actually uses my education. I finished grad school. I have my own place and car, family and friends who love me, and a great trip to Cambodia coming up next month. There is no reason I should be depressed, yet here I am. I want answers. I want to actually have my serotonin and dopamine levels checked. I've been medicated for fourteen years and never had this done. I'm glad that I'm functional. That's better than not being functional. However, I want more. I want to be happy. I want to not have negative thoughts daily. Just really feel happy. It's that too much to ask?