Can you tell me how to stop getting so sad and emotional at night?

Again yesterday night, while trying to sleep I was feeling sad and suddenly some sad romantic songs were coming in my mind and I was again sad about the fact that I am getting older. I am 21 btw and it sucks and I am embarrassed to say that almost tears came in my eyes again but I tried to control it. I also miss some people. At morning and the full day I am fine and happy but at night, I get all emotional.