I Have A 32 Year Old Son That Developed Severe

I have a 32 year old son that developed severe knee pain in one knee. Then his joints got really stiff, especially ankles, elbows and knees. Then came a fever, headache and chills. He went to the doctor and has had several tests with all showing negative except for inflammation. His level is 46. They are testing him for Lyme and rheumatic fever. His dr. thinks it might be rheumatoid arthritis. He is taking Naproxen but if he stops it comes back. He works at a busy truck brokerage and also has a small farm. Can exhaustion and stress cause this?