Bladder problems 😭

Since I became sexually active I had a couple of urine infections, my most recent on was so bad that it left me with awful symptoms after it had gone, it's like pain and pressure when I wee and I often find that I struggle to get all the wee out of my bladder. I have had multiple antibiotics and the doctors say there is no infection, I have had an operation to widen my urethra but that also didn't work. They have now just given me pain relief tablets but again it is not working. I am at a complete loss I am only 19 years old and I'm so worried about it now and the fact that it might never go away is a horrible thought, I was just wondering if anyone has ever had this or is suffering with it and whether there are any things to try and help? I've tried chemical free toilet paper and shower gels which changed nothing, I don't drink loads of cafine, cranberry juice doesn't work. It also hurts loads during sex like a stinging feeling and often I have to stop half way through due to the pain. Again this was all after a water infection that I got from sex about two years ago😭 Any advice or encouragement would be much appreciated! Thanks guys!