You have "left-side Ulcerative Colitis" or Proctosigmoiditis, like I do. Proctitis is only rectum involvement. As such, a suppository is likely not enough for you. A rowasa/salofalk/pentasa enema would be much more effective, and cover more area. Admittedly, with that many bms a day, you would be unable to retain the retention-enema for a full 7-hours though.
Learn everything you can about
your new Ulcerative Colitis diagnosis. And know that there is a lot of initial trial-and-error in treating UC. Your doctor will not necessarily get it right the 1st time, 2nd time, and sometimes even the 3rd time. There is no one-size-fits-all treatment for UC, as people respond so wildly different to different treatments (what's one's miracle cure, does nothing for another, and even makes another's symptoms a whole lot worse). Just know your treatment options, what is appropriate for your symptoms and disease extent and severity, and don't be afraid to suggest things to your doctor. We often find we need to become our own best advocates for what we need to be well. We become partners with our doctors in determining our treatment path. Sometimes we disagree with our doctors on a particular approach. No doctor-dictators allowed
You mentioned diet and that helps some, does nothing for others, and even makes others symptoms a whole lot worse. When you're flaring that badly, 20+ bms a day, it is going to be really hard to tell if anything food related is helping you. I would wait until your symptoms are more manageable before delving too deeply into diet for now. Diet did nothing for me. Some do swear by it, results vary.