Hi There I Am 30 Year Old Male...abt 2 Years

hi there i am 30 year old male...abt 2 years ago i started feeling this heart related problem...whn i was sitting on sofa or doing smething my frm nowhere starts racing and i have breathe so fast its like i am on a treadmill...5 months ago i never felt pain with these attacks but now it starts with a 3 or 4 second pain on my left side than the pain goes and heart starts racing for 1 min to 30 seconds than goes back to normal...and whn i exercise after i stop it still beats around 120 hours after i have stopped...and every now and thn i feel slight teasing on my left wich doesnt last long bt it scares me...i had 24 hour ecg but nothing was found...it really concerns me as i was a athlete 2 years ago...and now i even dont go to gym bcaz of this heart rate being high fr too long after exercising...i was divorced 2 years ago wich took a lot out of me but now am ok bt this heart problem is not going anywhere...plz reply...thanks..