Don't look to others for self-worth.
As for the depression, make sure you're eating well and regularly, getting enough sleep at regular intervals and get some kind of exercise. Some people are just more sensitive to this stuff than others. A lot of health stuff peaks around this age, too, so you may have nutritional or other physical needs that weren't as significant as a teenager.
Make sure you take care of yourself physically before declaring yourself depressed. Hopefully, this is just a temporary state brought on by stress. Of course, if you try to tend to your physical needs and really can't, then that may well be a sign of depression and you should definitely seek help.