Living with cystitis

Had radical prostatectomy winter of 2016, followed by 37 radiation treatments in the area. PSA has been fine, but the urgency to urinate has increased. A little late for my Urologist to say, “Oh yeah, the radiation has caused small blood vessels to increase in the bladder. That happens with radiation in the area. He called that Cystitis. After two scope examinations into the bladder- what fun-, no change in condition, and fortunately no blood in urine either. Taking Oxybutinen to reduce urgency. I was told caffeine is a big no-no. Might as well drink nothing instead of decaf. Anyone have experience with the condition, and drinks or food that irritate the bladder?