GP saying it's low blood volume, but not POTS?...

Hi all, so I've had POTS like symptoms my entire life, but it's gotten way worse since starting a more active line of work and it is really affecting my quality of life at this point. I mentioned my symptoms in passing to my psychiatrist and said it sounded like POTS and encouraged me to see a GP.

I saw a GP on Friday and she did an EKG which came back normal. When I explained my symptoms (without mentioning the POTS theory) she said it sounds like I have low blood volume and told me I should up my sodium and electrolytes. I asked if that meant I could possibly have POTS as that's what my psychiatrist mentioned. She said she was not familiar with POTS, but told me no I probably don't have POTS because POTS is a diagnosis by exclusion for when fainting can't be explained by anything else?? (her words, not mine) I'm really confused about what she's saying with the low blood volume/take electrolytes thing because it sounds like she's talking about hypovolemic POTS without calling it that?

Anyways, she ordered all the same blood tests I've already had done by my psychiatrist and is convinced something in those will be magically different from the last test, so frankly I'm not sure she's going to be able to help me at all anyways... Should I ask for a reference to a cardiologist or different specialist of some kind? I feel totally in the dark and am just trying to figure out what's going on, whether it be POTS or something else. Any advice is appreciated.