Heart problem or out of shape?

I'm 19 years old, and I'm not sure if I have possible heart problems or am just really out of shape. Whenever I do any type of cardio activity (riding my bike even short distances, jogging or running, tae bo type exercises) I start feeling terrible and end up having to stop after only a few minutes before I pass out or something. I get lightheaded/dizzy, short of breath, my chest starts hurting (cant tell if its my heart or lungs), I start feeling weak and shaky, and the blood feels like its POUNDING inside my head. So then I stop and sit down to rest and I feel terrible. For minutes afterwards until my body completely returns to normal resting state I still feel lightheaded and stuff, and I sometimes get nauseous, and feel like I have a slight headache, and am sensitive to light and stuff. I've never heard anyone else I know experience anything like that so I began looking things up online, and most of the sites I've seen has had these symptoms related to heart problems. My friends dad is a doctor and says it sounds like I may have a valve or something that isn't closing all the way or whatever, and I found out from my mom that my grandmother did have the same thing, so I didn't know if that could be causing my problems, and if it's something that can be fixed. Or could it be a more serious heart problem? Also I wasn't sure if it could all be caused by the fact that I am really out of shape. I'm thin (only a size 6/7) and everything, but throughout my life I've never really been into sports or any kind of physical activities at that. But I wasn't sure if simply being out of shape would cause such symptoms like that. Any help or advice you have would be great. Thanks! Tweet