I think you need a different doctor! Someone who will listen to you.

You know your body, he may be a doctor but he's not in your head

I'd start with keeping track of what you eat and how it makes you feel afterwards. it could be a variety of things like food allergies (ie lactose intolerance or gluten intolerance) or it could be something like acid refulx. definitely talk to your doctor about it and if he denies you any of the tests make sure to stand your ground and maybe even pull the "Write in my chart that i have complained to you about these symptoms and that you refuse to treat me" or even seek a second opinion. I had similar problems and it ended up being celiacs!

It could be a part of the issue. You could also have Crohn’s disease too which effects your digestive system . Maybe you should try to find a doctor that wants to really help out.

Get a new doctor!! Find one that validates your experiences and makes an effort to find solutions