Had my thyroid tested and it came up negative but I found out tests came back neg but still be positive.
Depression for sure. I just started Zoloft a montha go but still tired.
Rather than an SSRI, try something like welbutrin. It boosts norepinephrine and dopamine levels rather than seratonin and gives you more energy as a result.
Check your sleep quality. You may be getting poor quality sleep and not even be aware of it. Talk to a doctor about it.
Check for allergies and food intolerances. The test for the former is an easy trip or two to the doctor while the latter requires some experimentation with elimination diets.