Perhaps be a bit more gentle with your ISC. I had all sorts of issues with slow flow , strictures and doing ISC, technically in my case it was intermittent self dilatation, rather than intermittent self catheterization. I needed to get the catheter through the stricture to keep it open, any further and it could cause damage to the bladder walls. Not sure how too gauge how far is to far, because urine may start to flow before you get the catheter through the stricture,if that is your problem. I did find I could poke around with the catheter without feeling any pain,hence the comment be more gentle. May be worth a conversation with you medical team.
Thanks Chris