I would suggest to see a Gastroenterologist especially if you have issues with digestion. There are many  cases where stress can bring on issues with your digestion and drs will prescribe medications that can help with that. Also, you may be going to the wrong dr. Its ok to get a 2nd or even third opinion to get down to the underlying problem. If you continue to have problems, I would absolutely see another specialist. Some drs will run tests and if everything turns out negitive, they give up instead of trying other things that may be  helpful. Ive been to 3 gastroenterologists and trust me, they all were ok drs but I finally found one that was able to get down to what was really happening with me.  Remember, drs arent GOD and they do make mistakes. When you sit and talk to them, let him know your frustration and Im sure you will eventually get to the root of the problem. Im not a dr but it sounds like you may have Irritable bowel syndrome. Look it up online and read about it. If it sounds like you may be having the symptoms, call a dr that specializes in digestive disorers.

Lotsa luck to you!

Robin