Question regarding Heart

[Lorentilly]

I am 22 and female, I weigh 9 stone and I have been having the feeling of thudding in my chest and neck every day, chest pains and random racing heart for around 1 year. I had numerous ECG tests (the monitor) and blood tests and they found nothing. I was then taken in an ambulance again last week with a heart rate whilst resting of 152 bpm. Months ago the doctors put this down to anxiety, the doctor now said he heard a heart murmur and it’s definitely not down to anxiety. I am on 1.25 bisoprolol. I can feel my heart beating hard even when it’s slow, this is especially worse after eating, and in a morning. Can anyone shine some light on what this could be as it’s so scary and the doctors don’t seem to know what’s wrong with me.

Thanks