I also had chest pain and arrythmia. I went to the ER at the hospital but they said nothing was wrong. The arrythmias lasted another 4 days! So I did more research and came across a book (on Amazon.com) by Dr Sinatra. He recommended L-Carnitine and and magnesium tablets and D-Ribose powder (a type of sugar which helps the heart muscle. After taking the Acetyl L-Carnitine and magnesium (I got these from www.iherb.com in the USA) my arrythmia and palpitation has gone and I am feeling much better. Living with arrythmia is not really 'living'. It is scary and you never know when it will come on. Before I started the tablets I was too afraid to go out of the house on my own. These natural products sustain and give necessary nutrient and biochemical substances to the heart and help it to alleviate the problem.
i suffered some of the same symptoms and thought it was my heart. had all the test that say its not though. i do have a fib but it wasn't causing my chest pain. long story short i went to a gastrointerologist and he sent me for a barium swallow which showed a spot on my esophagus that is the reason for my chest pain.
Do you feel any palpitations? Or unusually high or low heart rate (over 100, under 40, respectively) when at rest? If yes, then you could ask for a heart monitor to document the irregularities. It seems your doctors have been unable to capture a period when you were having palpitations, this is quite common and that is why the wearable heart monitor was developed.
Hope you get more help from others, and welcome to the heart rhythm community.
I see you live in the UK, and worry now that the US is trying to emulate the "great British health care system", we will soon see similar problems in getting to specialists - where I note your statement ".... finally saw my cardiologist...".