Strange symptoms, no diagnosis

I am 25 years old and have been struggling with tachycardia and fatigue issues for 4 years.  I have no family history of such problems, don't have any history of substance abuse, no history of mental illness, have a normal weight, non-smoker and do not have any other known underlying conditions. I was in very good physical condition until symptoms started suddenly when I was 21 (I typically ran about 5 miles per day)  I have seen numerous cardiologists and not one of them has been able to give me a positive diagnosis.  Here's the vital information:

-Normal sinus rhythm, resting heart rate of ~70 bpm.
-Sinus tachycardia on moving from a prone position to sitting or standing, generally an increase of 30-40 bpm.  
Tachycardia also present on minimal physical exertion (climbing stairs, walking)
-Frequent fatigue that is not relieved by sleep or resting
-Dyspnea while lying down and with minimal physical exertion.
-There are no structural defects in my heart (confirmed by 2 stress echocardiograms), no electrical issues (confirmed by multiple EKGs), all lab work is normal (anemia ruled out, adrenal abnormalities including pheochromocytoma and adrenal insufficiency ruled out, lupus ruled out, thyroid problems ruled out, CBC normal except for consistently elevated eosinophils probably due to allergies, reactive hypoglycemia ruled out), Postural Orthostatic Tachycardia Syndrome is highly unlikely
-Symptoms somewhat alleviated by beta blockers.  

I have stumped every doctor I've seen.  They all tell me that I'm in normal physical condition and there is no detectable pathology.  Basically, there is no reason for me to be having these symptoms.  Does anybody have any suggestions as to what could be behind all of this?  

[evo123]

Can I ask why you have been told that POTS is unlikely.  The diagnostic criteria is a hr increase of 30bpm or to 120bpm on standing.  

Please visit the Dysautonomia (autonomic dysfunction) community pages and see if anything sounds familiar.  

[NTB]

hi, just some thoughts about two things seem to stand out:

"symptoms started suddenly when I was 21"  Did you have a bad virus cold at that time? Did you move to a new home or work place? Did you travel anyplace where you might have gotten an exotic parasite or infection?

"consistently elevated eosinophils"  What if whatever is provoking the eosinophilia is also creating endothelial dysfunction, and that's causing poor oxygen transport to tissue? What's your BP, especially diastolic? (Though I'd assume it's normal since you're very thorough.)


Also, have you tried to see what happens with diphenhydramine? Or Singulair (I don't know of any OTC leukotriene blockers),or bronchodilators?