Thanks for your query.Based on the facts that you have posted it appears that you have a free mobile Testis. There is nothing to worry about as -3 percent of population have free mobile Testis The pain that you have may be due to associated Varicocele
which can be confirmed by Colour Doppler Study ..
Take some pain killer like Brufen
400 mg daily This is available over the counter.Antibiotic has little role to play in treating Varicocele.