What Do Recurring Chills, Sweats, Weakness And Body Cramps Suggest?

My husband has a recurring illness with flu like symptoms. He gets chilled to the bone but sweats profusely. He cannot keep fluids down so he gets body cramps. He s very weak. We ve been to the ER several times, they only give him fluids and send him on his way. Doctors have done bloodwork but not finding any cause. This has been going on for at least 3 years. This latest episode is the worst. It started 3 weeks ago and he s not recovered fully. He has the terrible chills and sweats once or twice a week but remains internally chilled all the time. Is there anything we should have doctors check for other than Lyme Disease?