Fast heart rate

Hello!  I'm a female, age 25, healthy weight, above average muscle mass.  I excercise regularly, using yoga as well as some Swiss ball excercises for my back, as I have some back problems.  I smoke, but I recently reduced to about half a pack a day, and only allow myself 1-2 caffinated beverages a day.  I drink less than once per week, no marijuana, cocaine, or other illegal or controlled substances.

Now that I have the background out of the way, here's my question:
My heart rate seems unusually high, in the mid to upper 90's most of the time.  I know that tachycardia is when your heart rate goes over 100, and it does that occasionally, but it usually stays in the 90's.  It beats faster right when I wake up, before I stand or do anything, usually goes down within an hour, depending on whether I have to drive to work.  I have no other symptoms, except that I have chest pain, but I was recently diagnosed with GERD, and I'm apt to attribute the chest pains to the GERD.
I have been to three different doctors.  I had an EKG done, blood pressure taken, and some blood tests for thyroid and cholesterol.  All of my tests have been normal.  My heart and lungs both sound fine.  Why is my heart beating so fast?  My best guess is due to pain, and stress.  I'm just curious as to whether the elevation in heart rate would stay this constant given just those two factors?
I really need help here.  I've been obsessively measuring my heart rate, which I know doesn't help anything, but I'm scared, frankly.  I recently was demoted at work, bumped down to part-time, and cannot reinstate my health insurance until June.  I can't keep going to the doctor only to have them tell me nothing is wrong.  This is sort of a last resort, because it really feels like something is wrong.  Is it the GERD?  Two doctors told me that, and one said I was having a panic attack.  But does GERD really increase your heart rate?  Should I give the doctor one more try?

[itdood]

That sounds like you're on the high side of resting heart rate but it's not out of bounds.   It sounds to me like you are obsessing over it too much.

There are automatic responses that cause heart rate to increase.  It's controlled by the central nervous system.  To be exact, the parasympathetic and sympathetic branches of the CNS raise and lower heart rate.  Things like digestion, standing up, waking up will increase "vagal tone", meaning signals will be sent to your heart to speed up.  Sleeping, relaxing, or just after an adrenaline event the CNS will activate the sympathetic nerves to slow the heart down.

The CNS even changes heart rate based on when you exhale and inhale.  You heart rate will speed up a bit when you inhale and slow down when you exhale.  It's called sinus arrhythmia and it's a good thing, it makes blood-lung gas exchange more efficient.

So anyways my suggestion is that you stop over monitoring yourself, chill out.  The anxiety from doing this can raise your heart rate 40% without you knowing it.