Most importantly you should see the specialist who can most likely give you a better answer. I understand with no insurance it seems impossible but it is your life, get a payment plan if you must, parents? grandparents? are you in college? go to the clinic at your school, but they willprobably tell you the same "see a specialiat."
Since you are young they probably do not think heart attack
or heart disease
, since they are more common in older people.
Mitral valve insufficiency or stenosis? abnormal heart beat
, enlarged atrium, chest pain
If you did not have the enlarged atrium I would think it was your anxiety
(heart pain common).
Obviously there is something else since physically there is a sign. Search for "Transitory Benign Chest Wall Pain" through google.com
There are two good sites wrongdiagnosis.com and ivillage.com, one has a board with other people asking a similar question like yourself the other has a symptom-possible diagnosis finder.
One more thing look up Metabolic Syndrome
I am a nurse but with your age and those symptoms there is so much more to know about you before a doctor can diagnose...past illness, do you smoke, overweight
, etc....That is what a specialist will figure out.