We're all human and we do become depressed over time. What you tell us is what you tell us, we're not asking you to tell us what your not comfortable with us knowing but the more information you can tell us, the higher probablility of us being able to help you.
I do know your concerns that your always thinking about where you'll be later in life, time to time i think that. What you haft to ask yourself, writing it down works better and gives you more of the big picture, is what makes you depressed. What things in your life makes you feel you don't want to be here. That is key is figuring out why do you feel depressed.
The next step is change, something in your life makes you feel depressed and what can you do to change it. Your concerned about the future, well what about the future are you worried about; earning enough income, being happy, your future social life? Regardless if you tell us or not you must find a number of possible solutions, it may not be as easy as I say. For example your worried about not being able to obtain good grades, solutions could include; taking time away from other things to study at night, changing your diet into a healthy one so that you're more focused during classes.
Also find what you're good at and interested in, those will contribute to you fixing your depression. We as humans tend to become more positive when we're doing something we are good at or like to do. Myself i really like working out at the gym, not only does it help me psycologically but it works physiologically and socially.
Hope you get better soon