Lots of good advice above. I was dealing with health issues last year and I was told by several doctors it was stress, possible early menopause. I kept pushing and it turned out to be that my heart was beating way too fast throughout much of the day, which caused exhaustion, and many other symptoms. This was diagnosed after me being pushy, and finally getting the right cardiologist. They were able to do a heart procedure to address the issues.
It took me a while to get the correct diagnosis, might be worth exploring different doctors to get another opinion.