I am 56, still menstruating, I am vegetarian, always active ...

I'm 56, still menstruating, 4 years I'm vegetarian. I have always been very active, I go for long walks, from 15 to 200km eventually, I also do trails in woods and mountains. In recent months, I have been too tired, so much that I gave up the gym, because I could not do the recommended exercises, even at home, I have been feeling too tired. Another thing, my nails flake, my hair is dry and dull. What recommendation do you have and / or which doctor should I consult? (annually I do chekUp with Gynecologist and Cardiologist, because I am hypertensive). Thank you!