That's the catch. Hard to say on that. Have you asked your Dr about other possible dx? Maybe they can do some blood work? There are lots of things that could cause exhaustion. Some as simple as low iron to being as serious as cancer. If you aren't satisfied with your dx, I would ask for further testing or a second opinion.

Sleep can absolutely impact every part of your day. Have you asked about a sleep study to look at the quality of sleep you are having? I would also have conversations ruling out other medical issues. Did you mention to your doctor you don't feel depressed just tired? It could be anything from apnea to thyroid issues. If you aren't feeling heard I would consider a second opinion

Yes I've had several blood tests and a sleep study and aside from a vitamin D deficiency that I'm managing with a multi vitamin, everything was normal. It's a bit frustrating honestly.

I think a good way to know is if you have been put on medication for depression, if you seem to be better after some time, then it is likely that. However, if you aren't noticing any change with medication, I would ask for a different medication to try, then if still the same, go back and ask for more answers.