19 years old, Severe Pain in chest and upper back causes vomitting and balckouts

Problem:
For the last two years, I have had an episode of severe pain in my chest about once a month.  
The severe pain is now constant.  The pain is located on either side if my sternum, staring at the part of my clavicle near my throat, and curves down to half way below my breast.  It is also located between my shoulder blades.

I have gotten an EKG, chest X-Ray, and blood tests when my pain is at its highest, but all were normal.

At its worse:
The pain gets to the point where I get extremely nauseated, hot, shaky, and weak.  I eventually vomit either until the pain subsides or I blackout.  I've noticed the pain increases if I sit for long periods of time, but walking doesn't help the pain. The pain wakes me up at night, and worsens in my chest if I lay on either of my sides.  It also worsens when I exhale, causing me to breath irregularly.  

At its best:
Taking 4 regular Tylenol every three hours dulls the pain enough to prevent vomiting and blackouts.  The pain is always there, but not a severe.  Exhaling or lying on my sides doesn't hurt.


Current Medications:
Birth Control
Tylenol
10 mg Adderall (adderrall) twice daily, every other day

Background:
I am a 19 years, 5'2" and 120 pounds.
Prone to Migraines  
I have a very high pain tolerance
I am a pre-med college student, so I am under a constant amount of stress and am constantly studying.
I have had slight Scoliosis since the first grade; there has been no change in degree since then.
I was in very competitive gymnastics from 7 years old to 18 years old.
I have broken my right elbow and my right ankle.
I have had persistent lower back pain for a couple of years, but nothing I can't deal with
Besides the ones listed above, I have had no serious medical history or problems


Please help me.  I have gone to countless doctors but no one can tell me what it is.  I don't know what else to do.  Do you have any suggestions or diagnostics?