Even though you say you have a healthy blood pressure, your blood pressure may fluctuate and, at times, drop too low. That's called hypotension.
Signs and symptoms
The cardinal symptom of hypotension is lightheadedness or dizziness. If the blood pressure is sufficiently low, fainting and often seizures will occur.
Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension:
Shortness of breath
Fever higher than 101 °F (38.3 °C)
Severe upper back pain
Cough with phlegm
Prolonged diarrhea or vomiting
Adverse effect of medications
Acute, life-threatening allergic reaction
Loss of consciousness
Temporary blurring or loss of vision
In some cases loss of hair
You are experiencing some of the above symptoms. Low blood pressure will disrupt the blood flow to your brain.
You also report that sometimes your symptoms occur when you stand up from a seated position, suggesting that you have positional, or orthostatic, hypotension. It is fairly easy for a doctor to evaluate this. They take your blood pressure when you are sitting, standing, and lying, waiting 2 minutes between each change in position before taking your BP again. Then then note any changes in blood pressure and heart rate with each change of position. When the BP drops, your heart rate may increase, since that generally happens.
If they determine that your blood pressure might be dropping too low, and causing your symptoms, they then then look at some of the possible causes for this to be occurring. As I mentioned in my last post, you might have a low blood volume, due to inadequate fluid intake or low electrolyte intake. If that is the case, increasing your water intake, and making sure you take in enough salt, may solve the problem. If that doesn't work, they might move on to investigate another possible cause. But you did mention that you take in a high amount of protein in your food. A high protein intake, particularly coupled with a low carbohydrate intake, will increase your urine output, causing your body to lose more water. That does suggest you might be prone to dehydration if you don't keep a eye on your fluid intake and your salt intake. In addition, perhaps you need to decrease the amount of protein you eat, and increase your carbohydrates. Simple lifestyle changes can make a big difference. You do need to speak with a nutritionist/registered dietician. You probably need to eat better, you need to put on at least 15 more pounds, and you need to take better care of yourself.
My point is, investigating these sorts of things does not require high tech medicine. This is rather simple, basic stuff, that any internist or pediatrician is able to do.
Perhaps you have to be assertive, and ask the doctor to check your blood pressure in the various bodily positions, if they don't automatically do it, but any doctor should be willing to do it.
Most likely, the changes in your heart rate are connected to changes in your blood pressure, or changes in the dilation of your blood vessels. If you had a problem with heart rhythm it probably would have shown up on your EKG. If there is any concern about your heart rhythm, the doctor can have you wear a Holter moniter for 24 hours to try to detect any irregularities. Even in a very small town, I am sure there is a Holter moniter available. Again, this is basic stuff, not high tech medicine. But it really is unlikely you do have heart rhythm irregularities--I think they would have noticed them on your previous EKGs. Mitral valve prolapse can sometimes be heard by the doctor when he listens to the heart, or it can be seen on a simple sonogram. But you said they have eliminated that in your case, and MVP does not affect heart rhythm, and really doesn't fit with any of your symptoms.
I really think that your problems may turn out to be due to your lifestyle--your eating habits, not eating enough, eating too much protein and not enough carbs, not drinking enough water and taking in enough salt, exercising too much given your body's energy level (which does, in turn, depend on your calorie intake). If you are 5 foot 4 inches tall, and you had to gain weight to get up to 94 pounds, and you only did that after a doctor told you to do so, you have not been taking proper care of yourself. You may be starving yourself and this may be the crux of some of your physical problems. Perhaps there are psychological issues you need to look at in terms of how you feel about your body.
You certainly do need to see a doctor. I really don't think you need a high tech state-of-the-art urban medical center. Pretty much anything you need done in the way of diagnostic testing can probably be done right where you are. I'm sure the people in your neck of the woods aren't dropping like flies due to primitive medical care. I doubt that you have anything really tricky wrong with you that they have never seen before.
But, while you are waiting to see a doctor, and a nutritionist, start making some positive life style changes. There are plenty of good sites on the internet where you can calculate the number of calories you need a day based on your age, your height, and your activity level (I suspect you need something in the neighborhood of 2000 calories a day, which must be a lot more than you are now eating), and they can break down how many grams of protein, carbohydrates, fat, etc. you need to take in, so you know how to divide up those calories. Start reading about nutrition, start educating yourself. Most of all, start taking good care of yourself. You can, and should, take charge of your health. If you start now, you will help to insure yourself of a lifetime of better health.