I see you titled your post 'prostatitis', and i think this is the likely diagnosis.
In men under 35 this is usually an STD and requires different antibiotics than men who have prostatitis from an enlarged prostate.
The typical treatment for men under 35 years old is Rocephin (ceftriaxone) as an injection and doxycycline, or TWO weeks of Septra (trimethoprim sulfamethoxazole).
Alternatively, IV antibiotics (ampicillin and gentamycin) are given a few times a day for two weeks which requires an in home nurse visit and a temporary indwelling IV line.
However, you now seem to be in the 'chronic' category of prostatitis, which, as you have guessed, takes a much longer course of antibiotics.... up to twelve weeks, usually Septra.
Also, since you now have testicular pain, the fact is that you need an ultrasound of the testicles to rule out Epididimo-orchitis, an infection of the testicles and epididymus.
HERE IS A LINK ON PROSTATITIS
HERE IS A LINK ON EPIDIDIMO-ORCHITIS
In short, you are right to be concerned. The diagnosis was missed initially and I do not think the first few providers who saw you did their due diligence. I would not hesitate to go back to A and E and tell them that you think you have prostatitis and epididimo-orchitis and believe you need treatment for this, and an ultrasound of the testicles. This sounds like it is getting out of control and this can, as you guess, be dangerous. Do not hesitate, print out the linked articles and DEMAND proper treatment now, as every day that your pain increases raises the risk of failure of treatment of spread of infection.
I am standing by if you have questions for me.