I question that POTS can be cured at all, but I've gone down both routes. If you go the natural route every single doctor appt, test and supplement will likely be out of pocket. The one GI test recommended to you several posters above is $500. It could cost thousands of dollars just getting the tests done and then you run around forums, Facebook groups looking to understand the results and trialing expensive supplements. If you are doing well on midodrine and ivabradine, then I don't see a reason to change it.
Some people have an idea that somehow prescriptions are bad, but supplements are good. It doesn't work that way IMO. Natural does not mean there are no risks involved in trialing them. Too many wrongly think that since it's an herb, vitamin or something 'natural' that there aren't side effects or potential problems. My husband was permanently damaged by a supplement.