Enlarged lymph node for almost 4 years. Difficult for doctors to feel. Painful mainly at night, chest x-r, blood test, ultrasound neg. Ideas?

Probably nothing. If it's been ther for 4 yrs. Where is it?
Watch and wait. You may feel the nodes every couple of weeks, if any of the lymph gland doubles in size, becomes painful, ulcerates, or other nodes become enlarged, or you develop fever, or lose weight, you should see a doctor.