I feel some exhaustion every evening. i'm a 47-year-old healthy man. what should i do to figure out what this is?

Start with a checkup: If you have access to healthcare, it will help to see a healthcare provider to get a general check up and do routine screening tests including blood work for anemia, thyroid function and vitamin D & B12 levels. Discuss any symptoms or concerns with the doctor to help guide your workup. Make sure you're getting enough rest, regular exercise, proper hydration and balanced diet.