I Am 60 Years Old In Very Good Shape. I

I am 60 years old in very good shape. I am a hiker, physically active. July 6th woke up with a very stiff neck. July 7th in the evening had a high fever, but it was gone by morning. Was tested for Lyme's disease, came out negative. On vacation in Connecticut, went to walk in clinic on July 9th. Went to a chiropractor twice. Just came down with another fever today, 102, took ibuprofen. I have not had a fever in 4 years. What could cause the chronic stiff neck & reoccurring fever?