There are many possible causes of diarrhea consisting of yellow stool with red specks. Yellow stool is a non-specific change that solely indicates that a rapid transit time through the gut and red specks can represent small amounts of blood or tissue.
While Candidal overgrowth can cause diarrhea, it would not be a common cause in someone of your age, unless there has been a need for chronic antibiotic use. The most common cause at your age would be a functional disorder of the gut, such as irritable bowel syndrome, or IBS. However, there is no test to confirm the diagnosis, so the diagnosis is usually made by excluding other possible causes.
From the perspective of overgrowth, a bacterial overgrowth is more common than a Candidal overgrowth. Another concern that can happen in young adults would be inflammatory bowel disease, such as ulcerative colitis or Crohns disease.
It is possible to have gallbladder or pancreatic dysfunction that presents as diarrhea. You are correct that it would be unusual for pancreatic cancer to arise at your age, but inflammatory disease or gallstones would be more common causes at your age.
It is also possible to get chronic diarrhea from food intolerances, but you have already eliminated gluten. Lactose intolerance is also very common, but it is also possible to be intolerant of fructose or artificial sweeteners.
Treatment is generally oriented towards the underlying cause, which is why an appropriate evaluation is important. Without an evaluation, it is appropriate to eat a large amount of fiber, about 25-35 grams per day, along with about 64 oz of water per day. It also would be fine to use probiotics if they had been helpful. Any further interventions
, though, would require clarification of the underlying cause.