I have POTS but it only got worse after I had to go off of antibiotics (due to the state I live in). Before that it wasn't too bad.
You can read a plenitude of causes, symptoms, treatments on Wiki. (Wiki offers citations so it's not quite the White Bread that some people think but it does need clarifying.)
I saw Lyme disease offered as one of the causes. Perhaps as you continue to treat it may get better.
There are also some physical therapies that might help.
About the IV---- in case you decide to do it. It's not always the treatment that ends Lyme disease. That should be your decision, though.
BUT----- I don't understand why you'd have to go to his office to get the infusions! Most doctors have the IV catheter placed in a hospital then assign a home health agency to oversee instructions, dressing changes and delivery of the medication filled syringes to your home.
You should ask him about that. (Somewhere here there is a fairly complete description of how that works. Found it.