Antibiotics usually start to work in about 48 hours but it could take a bit longer. You said today is the third day, give it another two or so and if it doesn't get any better go back in to see him. He can run a blood test called HCG which shows up if you have testicular cancer. It's a hormone in woman that increases with pregnancies and men shouldn't have it but do with testicular cancer. You probably have an infection but if your really concerned I'm sure the doctor can do some testing to reassure you.
Good Luck!