There are a number of disease conditions which can cause such fatigue or loss of energy, like diabetes, thyroid problems, etc. You need to have a thorough checkup to rule out all such conditions. Tests that you should discuss with your doctor are:
Random blood sugar
Serum cholesterol triglycerides and their fractions.
Serum Sodium and Potassium, Calcium and Magnesium
Vit. B and Vit. D levels
Thyroid hormone tests.
Test for occult blood in stool
US of the whole abdomen.
Liver function tests.
Kidney function tests
Cardiac function tests
Till then you should take the following steps:
Try to avoid stress - cut down on coffee, alcohol, smoking.
Regular hours of sleep.
Good healthy diet. Take lots of natural instead of processed foods, cut down on sugar and carbs, take a low salt diet.
Iron, Vit. C and Zinc supplements
Exercise regularly, this is the most important step. Go for 30 minute walks 5 times a week at the minimum.
These steps will help but you need to get the checkup done.
If chronic diseases are ruled out, you could be suffering from a condition called Chronic Fatigue Syndrome.
Chronic Fatigue Syndrome is characterised by extreme fatigue which is aggravated by exercise, pain and weakness of some muscles, tenderness at some points, headaches, nausea, dizziness, sleeplessness, loss of memory or concentration and flu like symptoms like sore throat, weakness, hypersensitivity to noxious fumes, etc.
The exact cause of this is unknown, but it is theorised that it could be a post viral illness. It is often associated with psychological conditions like depression and anxiety.
Discuss with your doctor about chronic fatigue syndrome if all tests are normal.
Hope I have been able to clarify the situation for you and helped in resolving your query.
If you need more help, please let me know so l can continue to assist you.
Thank you and I wish you the best of health - stay safe!
Dr. P. Jyoti