Please push them. Not many doctors are aware of POTS and it is common for sufferers to go years without proper diagnostic testing and supportive treatment. Therefore they are sufferering more so. I have had a nightmare of a time trying to be seen by a doctor who knows about these conditions, as have most on this forum.
You sound like a Tilt Table Test would definately be the next step for you. Aswell as ruling out of other conditions. If it is another condition causing these problems, treating these would ease or even treat the dysautonomia symptoms. I cannot stress to you enough the importance of being seen by a specialist who is familiar with this. Every doctor I have encountered either has little or no knowledge of conditions of the autonomic nervous system unless they accompany a common illness like diabetes etc.
I have bradycardia laying and I have POTS as I have a heart rate increase of 30-bpm or more when standing. This is the diagnostic criteria. See this link below:
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia--POTS-Diagnostic-Criteria/show/1011?cid=196
Also, I am not sure where abouts you are, but if you would like to let me know I can help you find a specialist who would be able to help you. If you are not comfortable with leaving your location on this board then you can private message me. Alternitavely, follow this link to speacialists in Dysautonomia:
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia-Specialists/show/717?cid=196
There are treatments that can be tried for you, although they don't always work for everyone and sometimes it is trial and error to see which help you. Here is a link to our treatments information here on med help:
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia-Treatments/show/171?cid=19
There are a couple of things you can do to help yourself. The first being fluid loading. Increase your intake of fluids, electrolyte drinks help many of us here so it would be worth giving them a try. Increasing your salt intake is also recomended but I would advise against this unless you are actually confirmed as having POTS. I wear compression stockings (thigh high) too. All these things help.
Sometimes having a baby can upset our bodies, is this your first? And for some these things do settle alone. But both pregnancy and surgery are factors that can cause POTS, so ensure your doctors are aware of this. Unfortunately, many times, it is up to us to educate our doctors on this so the more you are aware the better. I am sorry for all the links but knowledge is power and we have to be our own advocate.
I sincerley hope that a cause can be found out quickly for you, please keep me updated with your test results and how you are x