What Causes Fever With Excessive Night Sweats?

My 35 y/o healthy son has had fever and sweats at night for over three weeks now. he has been to dr and has some initial blood work done. Circulation in his hands sometimes weird . Negative stress test. Liver and lymph numbers apparently high. They have tested him for mono, TB, strep all negative. They performed a second round of blood tests, my daughter -in-law, not sure what what was done still waiting on tests. She says he looks better but still feels drained and night sweats and temp. He has young babies of initially he was not getting his rest and went to work sick. They will be checking him for Hepatitis and lyme if the last blood work in neg. I can t imagine what could be going on? He is a non-smoker, non-drinker healthy guy.