Have you done a tilt test? You can do a poor man's version yourself if you want (lie down for a while then stand up while measuring your heart rate for 5-10 minutes (if you can)). An increase of more than 30 beats per minute is indicative of pots.
I'm actually just on extra salt and water with an exercise regime at the moment as that's enough at the moment. I'm also still breastfeeding and I find I do much better while breastfeeding.
I have also found betablockers to help in the past. There are a whole range of medicines available now. If you haven't already you might want to have a look at the DINET website. They have a good overview of different medicines, and also recommendations for doctors with experience with autonomic nervous system problems, and information you can point your own doctor to.
I'd heard the recommendation to increase salt and water before but I never really got any benefit from it until I did it with supervision from my doctor. We found I actually need to have around 3.5L of water a day and considerably more salt than i was (I was on salt tablets for a while).
Increasing salt and water is definitely the first and easiest thing to try. The idea is to increase your blood volume so that you are less bothered by drops of blood levels to your brain.
There are also exercises you can do to help strengthen muscles to help the blood keep going to your brain, really any general cardio (you can do it lying down too) and resistance training for your legs will help but there's also a specialized program made by Dr Levine.