If you're sincerely convinced your physician isn't taking you seriously, there's nothing wrong with getting a second opinion from someone else you trust (perhaps at a major medical center or university hospital).
But have you honestly considered the possibility that your doctor may be right, and your symptoms may be caused by stress? I'm not a doctor, of course, but I do know that stress can lead to a number of physical problems and symptoms. Our bodies and our minds are closely linked to each other; when something goes wrong with our minds it may affect our bodies also. (The opposite is true, too; when we're sick, it almost always affects our outlook on life.) The Bible says, "A cheerful heart is good medicine, but a crushed spirit dries up the bones" (Proverbs 17:22).
How can you deal with stress? First, identify it -- not only that it's part of your life, but also what may be causing it. Then ask God to help you accept the things that may be worrying you and not fight against them or let them grow in your mind.
Most of all, learn to turn them over to God. God loves you, and He can be trusted with every detail of our lives, including the things we can't control. Put your confidence in Christ, no matter what problems you face. Then you will be able to say with the Apostle Paul, "I have learned the secret of being content in any and every situation" (Philippians 4:12).