Have you had a urine culture test?
Really, you should have your urine cultured to find what the bacteria is, and which antibiotic it's sensitive to. It takes about 3 days from supplying a urine sample to having the test result, before that can know which antibiotic to use. Randomly trying different antibiotics is not the way to treat a UTI.
You might have prostatitis. Pain in the prostate often gets referred somewhere else, tip of the penis and/or testicles, because your brain doesn't recognise the prostate as a source of pain. Prostatitis can be hard to treat, and your GP is unlikely to do so successfully. You will probably need referring to a urologist, and even then, it's difficult to find urologists that are specialists in prostatitis.