Hello!
I read your question and understand your concern. 
I think that the symptoms you describe may be related to a possible rheumatological disorder 
depression. 
Have you measured your blood pressure ? 
Extreme fatigue, light headedness and fainting may be related to low blood pressure or chronic anemia.
An adrenal gland insufficiency and 
fibromyalgia could also cause similar symptoms. 
I recommend you to consult with your GP and perform a routine 
blood test, blood electrolytes, cortisol plasma levels and closely monitor your blood pressure. 
 Rheumatological tests ( like ANA, ANCA, ENA, sedimentation, 
Rheumatoid factor, etc) are necessary to exclude 
connective tissue disorders. 
Hope to have been helpful!
Greetings! Dr. Aida