Ed, I had a retention infection about a year ago as well.
I spent 5 days in the hospital on every antibiotic known to man.
At one time they cathed out 1000 cc as well. Since then I have been able to void OK. I have a stricture (scar tissue at Neo to Urethra connection) that requires me to cath every other day. I was worried about a floppy stretched out Neo as well. My Neo seems to be fine, and after voiding my cath amounts are under 100 cc, which is where you want to be. Usually about 40-50cc.
If you are having trouble going, maybe you have a stricture as well.
As far as cathing, use what is comfortable. FR14, 16, what ever works best for you. Lube them up good. It is much easier if you don't have a prostate as well. Baird French tip 14 works best for me. I have a prescription for four a month, so like Mike after a week (3 uses) they are tossed. Good luck, and yes, seek help from your professional.
Just a minor set back. Keep the big picture in mind.
Jim