Depression is often misunderstood.
Many people think that "depressed" just means "very sad". This is wrong.
Sadness is like water. It builds up inside of you, but you can let it out by crying.
When someone is sad, they are usually sad because of something that happened in the past.
Sadness is temporary. Like water, it comes and it goes, sometimes very quickly.
Depression is like a vacuum.
You can't just "let it out", because, being a vacuum, there is nothing to let out.
Depressed people don't care about the past or the present.
Why? Because they have given up hope for the future.
They accept that their future will be bad, either full of pain, or full of failure.
They feel unable to do anything about it. They are resigned to feeling hopeless.
Just as sound cannot travel through a vacuum, the vacuum inside a depressed person encases them in a wall of silence.
They isolate themselves, for they are in great pain, and have given up any hope of other people helping them.
Depression does not come and go easily. It creeps up on you over a period of time, and takes awhile to heal. Even after healing, it can come back if you are not careful.
If you feel tired all the time, lack interest in anything (apathy), and generally feel unable to move forward in life, then yes, it might well be depression. I would advise seeing a doctor about it.