Delora,
Sounds so challenging for you and the docs.
Glad the cultures were negative. Two things popped in my head. Above you is right, sex can continue the reinfection. It is the "milking of the urethral tubing (where urine comes out) that is the contaminating item.
Having a clean genital area and then URINATING immediately after sex is a very good way to prevent this. Now I am not saying this is your problem, I know I had to learn this early in my life.
"honeymoon cystitis" is an ecoli problem causing blood to show from the bladder wall and is VERY uncomfortable. Once I had the "rules down"....no more issues.
Now as we age the canal is changed with children and muscle weakening and that can give that other posts complaint of going and then leaning forward to continue to empty. The muscles of the abdomen are weakening. Keagal exercises with tighting and releasing the pelvic floor and tighting and releasing the abdomenal ones too may help.
IC( this is tough diagnosis) or really irritable bladder (for us) is part of FM. I get real complaints by the bladder when my back muscles have been pushed over the line. Pressure and frequency start but I am really fine...once I treat my back and rest I am in a better place.
I hope you get this sensation issue figured out, as I know so well how uncomfortable it can be. Good luck.
It is hard to find the right fit doctor...try looking into this book I use.
"FM and Myofascial Pain; a survival manual, by Dr Devin Starlanyl. (amazon.com) It has so much information for the many complaints we have and how to use tools to help yourself. I have also brought it to the doctor and showed her to help explain myself.
Good luck, Nancy B