Could be low B12. Maybe get a full spectrum blood test? Medichecks do a Well Woman test that covers b12, iron, haemoglobin, vit d, thyroid, oestrogen.
I had extreme fatigue and hair loss on hrt, the above test revealed low B12, low vitamin d and low haemoglobin. Am recovering now but it's taken months. Hope you get to the bottom of it 🍀