Research "cavitations". I had the same symptoms and it was from several infected root canals. It's a bone infection. They are very low grade infections but make you chronically tired and the lymph node swelling is a classic symptom. Hard to find a dentist who is knowledgeable on this, conventional dentists deny this even exists even though the infections have been proven. When I had surgery on my jaw, they found a huge pocket of infection and sent a biopsy to a lab that confirmed the type of bacteria it was. Just something to explore if you have had root canals in the past.