I get very sad as the sun goes down.?

Hello, I have noticed the past few weeks I've been getting this very DARK, achy feeling in my chest as the sun goes down and for the rest of the night I am VERY VERY sad. A month ago my gma passed away, IDK if that has anything to do with it. I am taking 50mg of pristiq. I want to seek help for this because it makes each night unbarable :( But I don't really know who to go to or what to say. anyone ever have this prob?