My Son Is 21 ,and Has Not Been Feeling Good

My son is 21 ,and has not been feeling good for the past 6 or so months. He has been feeling with fatigue and joint pain. He's had blood tests for lyme, thyroid, diabetics. And just recently had a swollen and red index finger on right hand. Dr. Prescribed antibiotic to rule out infection. But we have been reading up on arthritis. There are so many different types is there a specifically test to ask for when he goes back to his Dr.?