Pretty much what is said above. But if you can find even a little happiness in life at times, your not depressed. Remember to see how you feel. I have a bunch of these symptoms a lot, but someone is able to make me laugh. As I have dubbed it, Just Feeling Insecure. So pay attention to your feelings as well.
I am diagnosed with depression. I never thought I am depressed, because I am a quiet person and don't like to talk about my life and my problems to anyone. I laugh when I'm with my friends or family, but I never talk to them if there is a problem. And there were many small problems and in few years it all changed me. I didn't notice it at the beginning and it was getting worse. It was fine when I was around people, but always when I came back home, where I was all alone, faw away from my family, I couldn't stop cry. I didn't care about anything, my studies, my job, my relationships. I prefered to stay home, stay in bed and watch movies. But I told everyone, how much I did every day, how was at work. I always lied about it and mostly didn't go to a job because I wanted to stay home! Every second weekend I was visiting my family and then I was ok.
I went to a psychiatrist and she told me I am depressed for years. I didn't expect it, but I am on meds now and I see a difference. So you don't have to cry or have no appetite, don't need to feel miserable all the time when you're depressed. But if you see something is wrong with you and you don't want to be like this anymore, the best is to visit a doctor and talk. You might be depressed or not - the doctor will help anyway!
Try taking a look at the Zung Self-Rating Depression scale, that can be found here: http://healthnet.umassmed.edu/mhealth/ZungSelfRatedDepressionScale.pdfRemember, self-diagnosis is not always a good route. If you feel that you are seriously clinically depressed, notify your primary care doctor right away, so that they can properly diagnose, and help you make the right steps from there.
Mental Illness is a huge thing in today's world, and something you should not be ashamed of.