Wanted to add something I have had a similar reaction ,and I found that I am pre diabetic, Hypoglycemia may be something you experience also, as you work out it could have the affect of lowering your blood sugar, do you feel better when you eat , I am also checking out Hypothyroid and Lyme ..Good Luck
Hi
Welcome to the MedHelp forum!
If you are easily getting fatigued with accustomed exercise level then hypothyroidism, diabetes, heart problems, high BP and anemia should be ruled out first. If you become tired after unaccustomed exercise, then it could be age related or just that you are not used to exercising and keeping drinks handy after exercise such as lemonade, juices etc will help. It would be good if you could get a complete body checkup, even if you do not have any obvious problem other than this fatigue. Hope this helps. Take care!