Hi Koigal,
I think you most likely received an ultrasound exam and maybe a CT/MRI. This is not uncommon because in women, a UD is not the standard exam. With ultrasound (depending on the machine) you can calculate bladder volume and see if there are urinary obstructions kidney problems or ureteral anomalies Unfortunately, you can't see the dynamic behavior of the bladder with it. Now, if you want to know more about the dynamic behavior of the bladder, urodynamics (UD) or also called cystometry (not cystoscopy) comes into play.
During a urodynamic exam, a catheter is inserted into your bladder and your bladder is filled with a saline solution under computer control. Basically, two sensors measure bladder pressure and abdominal pressure during the filling process. The doctor will then ask you when you feel the first urge to urinate, when a strong urge to urinate sets in, and when they almost can't hold it in. Depending on the bladder pressure, uncontrolled emptying may also occur (which is intentional). In addition, bladder capacity, voiding speed/volume, and muscle contractions are measured.
With these data you get a very good insight into the dynamic behavior of your bladder and can include or exclude causes. This method is very suitable for the diagnosis of bladder / sphincter anomalies, pelvic floor problems and urinary retention and gives indications of neorological problems. It basically provides information about the interaction of the bladder and sphincter, bladder pressure and bladder capacity, and bladder sensitivity.
However, it does not provide information about the condition of the bladder wall and the GAG layer itself - which is important for the analysis of a possible interstitial cystis. For this, a cystoscopy is necessary. A cystoscopy is an examination in which a catheter is also inserted into the bladder and a camera is used to examine the inside of the bladder.
Both of these exams are necessary - in combination with an extensive lab - to get a better diagnosis in the case of IC. In some cases, a neurological exam is also necessary - especially if nerve damage is suspected.
So to be honest - I would not trust any doctor to make a "general" diagnosis or a very specific (like) IC without these exams.
I was foolish enough to trust my first doctor here and learned the hard way that not everything doctors tell you is the complete story. Unfortunately, it seems that you have to take care of a lot of things yourself - otherwise you waste a lot of time that you might need to treat the root cause.
I think that's what a forum like this can be helpful for. Therefore, I can only recommend everyone to ask exactly and to have everything explained to you. Many things seem simple and logical at first - but unfortunately it is often not. Especially with topics like IC or chronic UTI, many people suffer for many years before the cause is found - and that doesn't have to be the case.