For me there are huge differences between being severely depressed (non functional), moderately depressed (functional but just going through the motions), and "normal". I can easily differentiate between them. Mine is cyclical though and I have been dealing with it my whole life so I know it well. Cyclical is different than long term, like something that lasts for a year or more.

Maybe the only way to know is to see if you possess the power to change how you feel. If you change your thinking about things and seek attention in positive ways rather than negative ways does it make a difference. Does changing your attitude towards things make a difference. Maybe some therapy would be needed to do this. Behavior can be learned and hard to break. I think if it is clinical depression it is a tougher nut to crack. Probably only you can answer it. Feeling sad and hopeless for that long is serious. Maybe seek opinions from professionals. I was a functioning alcoholic for many years but the fact that I functioned did not mean I was not an alcoholic.

I have also functioned with moderate depression most of my life with periods of very severe. The fact I functioned did not mean I was not moderately depressed. I think we all want a reasonable amount of happiness and satisfaction in our lives. Going through life sad and hopeless but functioning gets very old and tiring.