That sounds familiar.  I'm 29 years old female, smoked about 9 years and have had the same problem from when I was 17 as a non-smoker.  I have as well visited many doctors who monitored everything from my blood pressure to a brain MRI.  I am as well 5'7 and I weigh 105 lbs.  I eat normally, however don't eat sugars due to allergy constraints.  One thing I did find out 7 years ago is I have a severe case of TMJ.  This condition has greatly affected my life, from external factors to a broken marriage.  This condition has: at one point taken my eyesight, which has returned, my energy, my ability to work, and left me with massive migranes to complete physical exhaustion.  All I can say is, yoga and pilates helped me immensely, I limit cardio to 3 times a week for short bursts, often bicycling or power walking wearing an earband and wearing  a biteguard at night.  If you have lower blood pressure, I think that doing lower impact cardio for longer periods of time probably will alleviate the chest problems you have.  I don't recommend fighting through the pain, I tried for years, and nothing has changed.