Sadness keeps going on

I have been sad and I don't even know why... Some weeks ago I had some problems with my boyfriend and since then I feel I am sad inside u know? We talked about what happened and everything came back to normal but this sadness is not going away...I just want to sleep, sleep, don't have guts to eat and if I eat I feel no pleasure...It's been month since I had not felt symptoms of depression...why is it coming back?