Should I Seek Colonoscopy Due to My Unexplained Bowel Changes & Low B12 Levels?

Hello, I am a 19yo male. Months ago, I had some neurological symptoms and went to hospital. There, a blood test showed that I had really low B12 vitamin (under 90 pg/mL). I had some shots to increase B12 levels and hospital adviced me to go to GP and have gastroscopy and colonoscopy to find the cause of the deficiency, because it was not normal at that age to have that low b12 levels. So, the days I was taking the B12 shots and planning to go to a GP, I had some bowel symptoms, including changes in stool size (small-thin and rounded / however not hard to pass), and rarely a little blood on them. When I went to the GP, I told him the whole story and told me that I had to do some other blood tests first to see if there is any gastric inflammation and then we would see if endoscopy is needed. After doing several blood tests (ECR, CRP, etc..) and faecal calprotectin test, GP told me that results were normal and did not show any inflammation in stomach or colon, so no endoscopy was needed. He told me that these symptoms were from functional gastrointestinal disorders and hemmorhoids. All of these happened like 6 months before. Now, I still have small-thin and rounded stools (rarely i pass normal stools but most of times they are like that) - blood is very rare and in small amount. Generally, my diet is normal (includes fiber), i drink a lot of water, no anxiety, not anaemic, normal weight and I exercise. So, these changes in bowel habits that happened months ago (without having any lifestyle change) + little blood rarely + the B12 defficiency I had, make me think I should visit another GP and push for a colonoscopy. I tried to search if increasing B12 would cause such changes in bowel habits, but did not find something. The only family history I know are that some first degree relatives had a small B12 defficiency without symptoms and second degree relative had gastrectomy a lot of years ago. I am a little panicked because Ive been seeing colon cancer is on the rise among young people and unreasoned bowel changes that dont leave soon + blood (however mine is very rarely and little) may be red flag. Especially most cases in young people are advanced stages becaus they are not caught early. Thanks for reading till the end, what do you suggest me to do? Go to another GP? And even push for endoscopy? Finally, could the cause of hard pebble stool be somehow (?) the elevation of B12 so my system need some time to go back to normal again? Because B12 deficiency was slowly developing for years.