ok first you may be suffering of some mental illiness, bipolarity maybe, who knows. if u go and consult well do it. u may get a prescription and you should be fine.

if not, if i was you i would concentrate on everything that is good and beautiful around you. remember your brain decides all. so try to convince your brain that there is no reason to be sad and depressed, and try to focus on all the good things u have. try just not to thing too much.

dont stay alone too. go see some friends, and talk. its always helping a lot just by the fact of sharing what u go through. try to smoke a bit and enjoy it. listen to music, try to meditate. who knows man, anything.

hope itll help and good luck, life is great, and bad moments are there to make u appreciate a thousand time more the good moments.

peace