What Causes Heaviness In The Chest And Breathing Difficulty While Having Heart Disease?

Hi! I m a 28years old male, and since last year I m having a heart problem( I think...).It started when I was on a diet .(In 3 months I ve lost 15kg.From 85 to 75 )During physical exercises or sometimes without any reason my heart suddenly begun to race even do I wasnt tired and as quickly as it started after couple minutes the symptoms were going away. So I went to a doctor I ve made some tests (ECG,Echocardiogram,blood,trademill) and everything came up normal . After that I didint have any palpitations but I was not feeling so good. Dizzines, felt like my blood pressure was jumping up (for example..when crouching) and down and heavy, slow beat of my heart . Now I m having tiny, needle like chest pains from each side and very cold hands, feet which I ve never had before. And on top off that for last couple days most of the time I feel like something heavy pressing on my chest, causing difficulties with breathing properly. I would be very grateful for any help or advice on this problem. Luka