What is the problem with my heart?

I'm a 28 years old I have cerebral palsy and had a seizure disorder. I've had a rapid heartbeat since 2001 when I was on Topamax. I've been off that medicine since 2004. I still have a rapid heartbeat. Went to the doctor he gave me Propranolol its not working. I also fell like someone is stabbing in the heart and the pain going to my back too. I'm scared to go to the dr and tell me that there is a hole in my heart. What do you think my heart problem is?