Just my opinion, but your very low resting heart rate is not a simple in office “ off the cuff” diagnosis of POTS. I am not familiar w that condition but read it’s symptoms on Mayo website. You need a new doctor and definitely look for your own electrophysiologist. I rely on multiple reviews and (where they did medical training.. it matters), when researching a doctor. Do your own, don’t rely on your current Dr. if you could go to Mayo Clinic, they have the BEST.