You wrote
A suggestion .. as far as I know and I maybe wrong .. in UK you have NHS which offers you a doctor of their choice .. the doctor who told you everything is fine .. what is his age and qualification .. MBBS and then MD/DM in cardiology? Since NHS is free you cannot say I do not want to be treated by the guy who came 30th in a class of 50 .. I want the guy who came first or second. In Britain a MD has a doctorate in medicine. Do not take word of anyone other than someone who is at least MD. Experience matters in medicine .. young doctors are likely to make wrong judgement .. doctors between 50 and 70 are the best."The pain with stress is around 3 out of 10 and without stress around 1 out of 10, but this is constant. I used to suffer quite badly from anxiety and although that has dissipated some what it is still dormant and can arise every so often.
I had a panic attack 3 years ago and had a check up in hospital which showed everything okay on the ECG and Echo, although I do sometimes have palpitations.
I have had other tests recently as it bugging me and they have come back all clear."
Please consult an expensive cardiologist .. someone with 1/2 FRCPs after his name and at least 25 years experience (making him at least 55 years old). In the long run it will pay off.
Once you develop some sort of arrythmia (irregular heartbeat) or ischemia (dead heart muscles) due to stress it stays with you for your life.
Take it seriously. Ask a doctor if it is safe for you to do medium exercise (such as brisk walking 5 kms daily)
Best of luck,