I'm sorry to read of your problems with retention. I have had what you describe for a decade. My retention causes chronic UTI's. I have had two bladder surgeries to raise it into position hoping to create a better flow. Both started out OK, but then quickly failed and my poor flow and chronic UTI's returned. I have been on low dose antibiotics of various names, but nothing would keep the UTI's from returning as a result of poor flow or sometimes complete lack of flow. Recently I have been catharized as an emergency in the hospital and in the urologist office. Both times I had over 500 cc's of urine that I could not void. My bladder would cause horrible levels of pain and it is scary. Since the two emergencies, I have been taught to self catharize.... not pleasant, but better than an emergency room visit and, as my new urogynecologist told me, better than having even more serious issues with my kidneys as a result of serious retention.
I have recently been diagnosed with IC/Bladder Pain Syndrome because I do not always have a UTI when I have severe bladder pain and the inability to void. I think I'm on the path to managing this condition, using a pessary, a daily dose of amitriptyline for pain, and self cath when necessary. I am feeling better because I feel like I have some level of control back with the use of self cathing when necessary. This diagnosis and potential solutions are all new, within the last month, so I can't be sure the results are long lasting, but I'm happy to have some time of no pain. Don't give up. Change doctors if you don't get answers. My biggest regret was staying with a urologist that just kept prescribing anitbiotics for over ten years.