Could somebody pleae give me advise on what to do?

I think you should go to a gastroenterologist. Your symptoms suggest a number of things, but not cancer. You could have h. pylori, IBS, celiac, or something else. Do you have any pain? One good thing try to that will likely help a lot with diarhea is acidophilus or probiotics supplements. It's the "good" bacteria that's found in yogurt and keeps the balance in your intestines.