My Depression?

Why does it seem that I go into a very depressed state after school or typically in the late evenings on weekends? Like I just feel generally bad and regretful... But what do I have to regret? What do I have to feel bad about? Maybe my "depression" is just my body telling me I need sleep because after I sleep I feel fine and those thoughts are gone with only a slight memory of them... I need to be happy again, I need to feel it.... And not just my burst of joy I get when a certain someone's actions surprises me or when I'm alone with this person, and i want to do ... Well what isn't spoken of or something generally with this person...but an everlasting joy that I can live with... Either Way this is a problem thats real for me and I do have some looking into to do...