What Causes Recurrent Flu Like Symptoms In A Bladder Cancer Patient?

My husband keeps having flu-like symptoms with headaches, fever and chills and overall fatigue and achiness. This happens almost every week. He has had many health problems - Wegeners Granulomatosis, heart attack, bladder cancer, Dermatomyocitis (as a child), sinus problems etc. He had an MRI of his abdomen because it has become somewhat distended. His bloodwork seems to be ok. None of the doctors have been able to provide a diagnosis about this latest problem.