What Causes Frequent Strong Heartbeats?

Hi, I am going to start for from the beginning. I am 28 years old male and slightly overweight. About 1.5 months ago i was playing soccer. During the game, pain started to develop right by the bottom of my lefts ribs, just abit southwest of the solar plxes. This pain was accompanied by slight diarrhoea the week following the soccer game. I saw a GI and he was convinced it wwas some sort of tummy infection. Stopping short of giving me antibiotics, he gave me just probiotics. This helped with the pain and diarrhoea. With the pain subsiding, all was good for a couple of days then i started to feel the extra strong heartbeat. It started off as once a day and now it s getting worse. Then having lunch 2 weeks ago, my heart gets 2-3 flutters in a row and i got into my first even panic attack. Rushed to the A&E and did an ECG, ECHO, Stress test and blood test and hoiter 48 hour texst. Which all came back clean so all the doctors gave my an all green to go home. Two weeks on.. the strong heart beats are more frequent and it s really effecting the quality of life. Could the upper abdomen pain be the cause and not the heart? what is going on?