Chest discomfort sometimes

I sometimes get discomfort in my chest/throat and sometimes its just my shoulders that ache. I cant tell what sets this off. Exercise can do, other times I can walk for several miles with no problems, sometimes I wake up on a morning with a tight chest. Mr doctor has done and ECG and blood tests, Thyroid is ok, Cholesterol is 4.3. Blood pressure when I took it just now is 93/71 - its seems to vary a bit though.

My doctor says my heart is ok he thinks and its anxiety, I'm not convinced by such a vague 'diagnosis' Im worried its angina or something like that.

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I found that my Angina was very variable. Some days I could walk for a long distance, whereas others I found it too difficult. You can't go by a cholesterol test anyway, many patients with CAD have low cholesterol. An ECG is not likely to pick up anything unless you have advanced disease and/or having an attack. I had loads of ECG's where I was laying relaxed on a bed and of course, no discomfort, so they looked great.
My symptoms started just like yours and for a whole year I was prescribed Gaviscon because they believed it was a stomach disorder. A chest x-ray, echocardiogram and ECG made them conclude it wasn't the heart. A year later, I had a heart attack.
I found that air temperature was a big influence on my angina, the cooler the air, the quicker and worse my throat discomfort became. If I tried exertion after eating, it was a lot more difficult too. I recently read some research where blood flow was analysed after different food types. I was told for example that Olive oil is good for you on food because the mediterranean countries have low instances of heart attack. During the research it was found that blood flow restricted by just over 30% from olive oil. The only foods which made no difference was fruit and veg. The only 2 tests which revealed I had a problem were a) a stress echocardiogram and b) an angiogram. Even a nuclear perfusion scan said I was in great shape and shouldn't be suffering angina. Rather than an invasive procedure like an angiogram, I think you would be wise to have a stress echo, which will put to rest whether you have a heart problem or not. Under stress the apex of my left ventricle was contracting more slowly than the rest of the muscle. From my experience I wouldn't leave it. I was 45 when diagnosed with a stomach disorder.