I can tell you are worried... I am sorry that you are not feeling well either.
My best advice is to be honest with your doctor and let him know what you are thinking. See if he is willing to do some further testing such as a Gastroscopy ( tiny camera down the throat into the stomach) and some blood work . If he won't, look for someone who will.
Just because you are 31 and don't drink much or smoke means nothing really as far as cancer goes but, I still think you need to know why you are not getting better.
Try not to think the worst though. There are other less serious problems with similar symptoms and the odds are that is your case. Take things a step at a time and don't stop until your mind and body are at ease. You know your body better than anyone.
Take care