You had scans though, depending on what scans you had I.e. a CT would have definitely picked up inflammation in the structure of your colon unless it was the smallest polyp that wouldn’t have grown quickly enough to cause the symptoms your having in such a short space of time. My Dr told me when I was younger that the NHS start screening at 50 because polyps tend to form in 40’s and then take 8/10 years to develop into something that could be described as sinister. Not eating is probably making you feel awful and making the stomach issues worse.