Rectal bleeding bright red blood, comes and goes dr checked for hemorrhoids found nothing what could this be?

Need to be checked : Sometimes bleeding from internal hemorrhoids can be difficult to determine if the bleeding has stopped or if the exam was done without an anoscope. Although internal hemorroids are the most common cause for painless anal/rectal bleeding there are other causes that need to be ruled out . Colonoscopy should be considered as a next step if that has not been done already.

Many possibilities: There are many possible causes for what you describe. This bleeding could start anywhere from your stomach to your anus. The most common cause at your age is hemorrhoids. External hemorrhoids are visible on a simple exam. Internal hemorrhoids require the use of a small scope to see them. If you don't have hemorrhoids, you will need to have a GI doctor check you out.