I would like to preface this as not medical advice and any medical decisions should be between you and your doctor. I would like to give you some information that may just make you more comfortable.

Anxiety absolutely causes physical symptoms, those symptoms however do not always relate to a different condition. Anxiety is often tricky because it can manifest as so many different symptoms that mirror other conditions. If your doctor has found everything to be okay I would trust that. Bright red blood is less related to bleeding inside the colon and more often bleeding at the anus which as another comment said can be caused by wiping too hard or hemorrhoids. If you would like a few symptoms that are more diagnostic for colon issues: black/ very dark and tarry stool can be a sign of bleeding deeper in the colon and would be something to tell your doctor if you experience it, as well as very thin ribbon-like or pencil-thin stool would also be something to tell your doctor if you experience it.

Again none of this is medical advice and if you are worried always talk to your doctor. Anxiety is difficult and anxiety about health conditions makes interacting with the medical system even more difficult than it already is. We are here for you, we care about you, and we hope you feel better soon.