Illnesses Anxiety Disorder which was earlier known as Hypochondria, is the agonising fear of being in some worrisome illness. Your fear about cancer could just be out of illness anxiety. On the other hand, you seem to be suffering from some kind of gastrointestinal disorder. A specialist doctor (gastroenterologist) will be able to take you out of your present symptoms which could be of a condition known as GERD or Irritable Bowel Syndrome (IBS) or even any other illness. Many illnesses of the intestine/ stomach like IBS are known to result in mental symptoms like anxiety and vice versa. I would suggest you to consult a gastroenterologist (if you haven't already done so) at the earliest, get diagnosed correctly and undergo proper treatment. This will also take you out of your (unnecessary) anxiety about cancer. After that, please consult a psychologist to get guided on coping with your anxities of these kinds.
Next Steps
Please consult a gastroenterologist and a psychologist thereafter.