Cystoscopy went well! Dr didn't see anything, but said urethra was pretty red. Prescribed antibiotic. Pain for 8mos now. Infections can last that long?

Not really. It is very unlikely that this is infection for this long. It is much morem likely an inflammatory condition such as interstitial cystitis or chronic pelvic pain syndrome. This is a benign condition which can cause persistent discomfort and pressure with voidign and in the urinary tract. Treatment consist of medical therapy, dietary changes, and analgesics.
?Interstitial c"itis. Suggest you see a urologist with interest in ic. Also check: www.Interstitialcystitisassociation.Com.
Urethritis. I agree, infx usually not that long....Culture results? Bx done ? More info needed.