How do I know if I'm actually depressed or not?

It really depends on the person. If you have a history of depression, the odds are you're more likely to suffer from depression. Generally speaking, if you're depressed you'll have an increased feeling of apathy and won't care about things you used to care deeply about. You'll likely stop enjoying things you used to enjoy. Not keeping up with your personal hygiene is another big sign as well, and you may start isolating yourself from others. If you have any signs of depression, talk to your parents and/or therapist about getting help.