Depressed people usually know something is wrong and they are depressed, yes. There is no mystery often when they suffer depressive symptoms.
How long has this been going on? Truth is, most people have bouts of the blues and little periods of time in which they are down. That's normal. And especially in the teen years. But if it goes on too long, it's best to talk to someone. The school counselor, asking your parents for help and find a psychologist that they can send you too, etc. So, depending on how long it's been, consider these options. good luck
Yes depressed people usually know something isn't right. It is sometimes easier for another person to tell if someone appears to be depressed for no reason, indicating it's a illness with one's body. That can be a hard change in point of view, because for the depressed person it's all very real, it is their reality.
I've experienced it enough times myself, where I get depressed, my reality changes to the world is a dark place and life is pointless, and everything is wrong about my world, and I have learned now to think, "What did I eat for lunch. Do I need some exercise? Go walk with a friend?"
Rather than think How can I fix my world, I now think, How can I fix my body?
Yes what you describe could be depression. Depends if it's been going on for a long time, and does it not make any sense, as in there really isn't a lot wrong, other than I feel awful, for no apparent reason, I just do.
Important to note if you do feel this way, there is hope, you won't have to suffer like this forever, there are many options, many things one can try, and usually eventually something works.
If it's a body out of whack cause, there are many medications that have helped others in the past, so likely eventually one of them you will find actually works wonders. There just is not any way to tell which one will work for you. You may have to try several before finding one that works for you.
But the point is there is hope, there are people who understand, and who can help get you feeling better.
Best wishes and thank you for asking! :)