High heart rate at rest and with exercise?

[firefawnakl]

So I'm looking for advice on where to go for assistance. I (suddenly) have a high resting heart rate and a VERY high rate when exercising. I was (until this started a few months ago) working out 5 days a week. Im not overweight (or under, Im right smack dab in the middle of normal). I eat 7 to 10 servings of fruits and vegetables a day and fast food is a never done thing. Ive never touched a cigarette, don't drink, and have never touched druga
Last year alone I backpacked the Grand Canyon 8 times to give an idea of this change for me, but on my last trip I noticed something....my heart rate was hitting 170, 180 on the way out and I kept having to stop. It got worse from there...I now have a resting between 90 amd 110. If I so much as walk to.my kitchen it can hit 130, and that's on a beta blocker that my cardioligist gave me (because the cardiologist and electrophysiologist are both at a loss as to whats causing it). So what Im wondering is has anyone else ever heard of anything similar? A test for adrenal tumors came up negative and my thyroid levels are in normal range allegedly. (The last specialist I saw found a goiter so Im waiting on imaging for that). Has anyone else ever had a normal heart rate suddenly go out of whack, with all tests coming up negative? Thank you for any help in advance. Ive seen 6 docs at this point and they all scratched their heads.