@n3tm4n , I had this problem very shortly after a Bladder Botox procedure. But, it wasn't every time? I assumed that it may have been some form of trauma from the procedure, although that didn't account for the intermediate nature of the problem. My final prognosis was the way I stored the catheters. They're in boxes, in alternate directions, one up then one down. And I was storing the boxes upright. So, I was putting a slight bend in the tube, right at the end. If that's not your problem, you may have a constriction. Advise your doctor and see if he can arrange a Flexible Cystoscopy to check it out.

@stumbler, many thanks for the reply. It hadn't occurred to me that I may be storing them in a way that may cause problems. My box is indeed stood on its end like a quiver holding arrows. I've given it a break for a few days, and tried again yesterday and was much more successful with just the normal slight discomfort but nothing more. Though I've also found out following tests I have an infection as well which probably wasn't helping. Anyway, all is well - both the Nurse and Dr appear unconcerned, and I'm much less stressed about it all. Thanks.