You're right you can't have cancer. Most people who have cancer is 50 and over so its impossible for you to have cancer since you're 19. Also your symtoms doesn't match the symtoms a colorrectal cancer patients would have either. Colorrectal cancer patients have: blood in or on the stool, a change in bowel habits, stools that are narrower than usual, general, unexplained stomach discomfort, frequent gas, pains, or indigestion, unexplained weight loss, and chronic fatigue. And did you try screening? It might be costly but its worth it if it could detect cancer. For yours you should try fobt (fecal occult blood test)screening, flexible sigmoidoscopy, colonoscopy, or/and double contrast barium enema. Trust me good luck! And hope you don't have cancer :)

You might ask your doctor about candida (yeast) in the intestinal tract. Antibiotics often destroy the healthy bacteria in our intestines and therefore yeast begins to take over. It often presents the symptoms you have (including extreme fatigue), and follows after one or two rounds of antibiotics. If you do have candida problems you can ask your doctor (or look online) for medicinal or herbal cures and an anti-candida diet. I have been on a herbal regimen for the past few months and have had great success.

I am not an expert and know nothing about the possibility of cancer. Iit may not be candida, but I experienced similar problems after antibiotics for sinus infections. It took me a year of going to the doctor to figure out what was wrong and that there was a direct link between taking antibiotics and my symptoms.

I hope it gets better!