My honest (and straightforward) opinion is that perpetual sadness is much like arrogance. Both require a lot of self-absorbtion. Arrogance has the "flavor" of being too proud or boastful in one's abilities, and the other has the flavor of being to negative. How do people treat you when you are sad? My best guess is that there is something about the way you are being treated that you really crave. If so, perhaps there's another, more positive way to seek fulfillment. Perhaps you could replace each "this is so sad for me" thought into a question, such as "What can I do to make the lives of others more joyful, today?" Sometimes, inner-happiness comes from not worrying about our own inner-happiness, and concentrating on others.

find someone to talk about it. talking about what has made you sad usually helps the sad feeling melt away.

you are probably a constant downer

I think that your unconscious caused this and you are enhancing that by repeating it, I am sad girl, I feel sad, I can't do it..etc so start to learn your unconscious, always say I am happy girl, I am strong , I am successful girl, I can do anything, I am on my right way. repeat these sentences and other positive sentence and write it on your desk, on mirror and on your room walls, surely you will feel how your life become better. I'm telling applied strategy which I used and I'm still adopting it.

you can do something interesting,and see some comic film,and then you will feel relax and happy. and you can smile now ,^_^,