Fatigue and tiredness. Keep myself fit.

Hi! 1. Post brisk walks, or low intensity workouts, I feel sleepy. Then I strongly need sleeping to address fatigue. I would need sleep to extent that my body is way over feeling of exertion After waking up, I don't feel refreshed. It is just feeling of resting, but then I don't feel any energy  to take up any other activity. 2. Regular office days (14 km one side travel on bike) with walking within premises (2k-3k steps), wear me out a lot 3. My yesterday's blood tests are normal. CBC, Vit D, B12 and RA factor are in normal range 4. I am mostly on vegetarian diet with fruits and salad, with occassional non-veg. I avoid eating oily foods. 5. My mom's side, there is history of diabetes, but I have not got at signs of it, based on yearly medical fasting and Hba1c reports I would like to know how can I address this issue,  since with age, I understand that I need to be active and doing fair amount of exercise to keep myself fit.