The symptoms you reported might be related to rheumatic fever. Rheumatic fever appears a couple of weeks after Beta-Hemolytic Streptococcus infection, usually located in the upper respiratory tract. When the infection is not treated well enough, then autoimmune processes might be triggered. Therefore, the body recognizes its own cells as foreign cells and tries to destroy them. This is most evident in the heart, the kidneys and the large joints (knee, ankle, and elbow). Since this condition is primarily caused by infection, antibiotics are always recommended. In your case, the only data that do not fit in are the negative inflammation markers. No data was given about which inflammation markers exactly were used. C-reactive protein (CRP) and Rheumatoid factor are just one of them. You might want to have another laboratory tests with these specific inflammatory markers included, when the condition aggravates again.
If the results are negative again, then there might be small bacterial focus that is very hard to reach with the antibiotic. These foci are sometimes located in the teeth, so you might want to schedule a visit with your dentist.