Your doctor may have suspected esophageal spasms, which can feel like heart pain and gastritis (stomach under left breast), but from what you say about your not being bothered by eating, etc. plus the acid fighters not helping, it might be the doc got it wrong.
If the doctor only checked your blood pressure and did an echocardiogram (or were you referring to an electrocardiogram- EKG)... in any even, they did not do thorough testing for your heart. He should have ran blood tests to rule out heart attack. Also, did your doctor order a fasting lipid blood panel? If heart attack is ruled out, they may want to do a nuclear stress test to check for any areas of abnormality, such as ischemia (lack of oxygen to tissues) in the heart. It is good to get your heart checked out, and if your doctor doesn't know the tests to order, it is best to get referred to a cardiologist who knows what they are doing. If your mom died of a heart attack or cardiovascular disease, I hope you have impressed that fact on the doctor, since family history can be very important.
With the tenderness and soreness you mention here, did you do any pressing on the chest wall where you feel these feelings especially? If so, it is very possible you have costochondritis (should be properly diagnosed by a physician, though, which I am not). I've had costochondritis diagnosed by a doctor, and it is very painful. I've had a doctor pin-point it with pressing on it. I've read it can hurt to take a breath with it even. It is an inflammatory process that can attack either side of the chest (I've had it on both sides) but many patients, including myself recently can think it may be their heart. Typically, when the doctor diagnoses this, they prescribe anti-inflammatory medication for this. You might think about what you might be doing to aggravate the problem (like leaning on your left elbow, for example) and try to avoid these things and rest it until you get to feeling better, if it turns out the doctor says you have this.