Something more than what the doctors say?

About two months ago I was taken to hospital with severe back pain, violent vomiting and it being painful to urinate. It was also painful when the doctor pressed my stomach. I was given antibiotics and told to go away, being told it was nothing more than a simple UTI. I took the full course of the antibiotics but as soon as I was off them it started again. Before I knew it I was back in hospital with even worse vomiting, back pain and all the same symptoms as before. I was just given more antibiotics and told to go away again. Weeks later and the symptoms still persist and get worse after sex. It's been a long time since I felt properly healthy. My mum suggested getting cystitis relief from the chemist to see if it'd help but it made no difference. I feel at a loose end and the NHS don't seem to want to know, anyone have any ideas what this could be?