Its called frustration, not depression. And, it is because you are not focused!! How can you go through all the hardship to get educated in the US, get a diploma but not know what you learned? But that is past. Lets talk about the future.

If I were you, I would get a blank piece of paper and write down what I want to accomplish in X number of years. Then I will write down what I want to accomplish in X+Y number of years and so on. Then, every night before I go to bed, I will make sure that I did not deviate from THAT goal, and every morning after I wake up, I will remind myself about THAT goal. I would work towards attaining THAT goal and believe that I will attain IT. Remember the story from Ramayana and Mahabharata; Rama and Arjuna hitting the target; the trick is to be FOCUSED!!

Good Luck with your grad school!! And this time, try doing your friends' work instead of having them do yours.