Hi Millie_
RH is a variable thing. Carb tolerances vary hugely, and so do RH reactions. Sometimes it is particular carbs (in my case gluten) that causes a worse reaction than others (in my case sugar or potato). Sometimes food intolerances look a heck of a lot like RH. Also, there are other medical conditions that display the same symptoms.
As
@Antje77 mentioned, you really need to have clear records of your blood glucose is you intend to take the evidence to your doc to push for further investigation into RH. I would suggest that you monitor your blood glucose before eating, then try to find out how high your bg goes (whenever that is), and then keep testing until you know when your bg drops to its lowest.
Then you can check whether your symptoms are tied to your blood glucose levels and discuss that with your doc.
You mentioned that you had a c-peptide test, and that you have the results, but you don't say what they are.
My experience of RH is that keto has helped tremendously, but if you were still experiencing your symptoms while you were strictly ketoing, and you have the blood glucose test results to show it, then keto may not be the answer for you.