The standard evaluation for men with symptoms like yours includes examination for urethral discharge and urinalysis, looking
for evidence of nongonococcal urethritis (NGU),
urinary tract infection (UTI), and prostate gland inflammation. (The latter two are rare in young healthy men, however.) But even those could be messed up by the antibiotic.
What to do now? I suggest nothing for the next 1-2 weeks, including no additional antibiotic treatment.