My Son Who Is 30 Yrs Old Has Been Sick

My son who is 30 yrs old has been sick with a virus for about 6 weeks. He went to ER twice due to Couldn't get fever down and was running 107.9.
ER said dehydrated and Low Pottassium and he did have Liver Damage due to being dehydrated for so long. He has been experiencing blurred vision in one eye and now lots of pain that feels like Pins and Needles in his hands. He's supposed to follow up with a doctor due to his Liver. What kind of doctor should he seek? And can a virus cause such a high fever 107.9 to last this long? What could he possibly have? He needs to return to work soon!