Get a PDF of the brief fatigue inventory. Read a study showing how the brief fatigue inventory was used with older adults, with good results about its usefulness. Get a PDF of the Chalder Fatigue Scale and read a post with critiques (namely, chronic fatigue patients rate "worst" right away and can't indicate when their symptoms get worse.) The CDC has a long ME/CFS symptom inventory that may help you organize and communicate about what's happening, or see that you don't share many of the symptoms of that specific diagnosis. I don't have any research or references on it. https://www.cdc.gov/me-cfs/pdfs/symptom-inventory-questionnaire-508.pdf
Click through for several formal inventories ("how does fatigue affect your life? how tired are you?") and links to research or critiques of them
Fill out the one that resonates and bring it to your doctor. If you don't have a doctor giving you similar inventories or asking these questions, the good news is you may be able to get better treatment somewhere. The bad news is you may need to seek it out proactively.