Cancer, how do i know if i have it?

My family has a history of cancer, and well, my moms dad had cancer [still has it] and my mom had cancer in her stomach when she was pregnant with me..I talked to my health teacher, and he said im at a higher risk for developing cancer.
My mother and...

father have smoked around me since I was born, and when they split up, my dad still smokes around me..
So I've been exposed to secondhand smoke all my life, and well, im skinny and fit and all.
I eat right as much as I can, and I workout 3 times a week.
Would that be enough to lower my risks of developing it?
Im starting to think I already have cancer, because I dont have asthma.
Yet I still get lightheaded, dizzy, touble breathing, and sometimes when I breathe deep, I can feel something weird inside my chest.
Also, I get these wierd moments where, I feel like im not breathing enough, and my heart starts to hurt , and my lungs burn.
I havent said anything to my dad about it because im afraid that if I do get checked out, and I do have lung cancer, that he'll blame himself..
Ugh, any advice?

See the doctor...we can't diagnose you, and putting it off would only make things worse if you do have it.

Well If I go to the Doctor, He probably wont do anything.
Last time I went to the doctor, he diagnosed me wrong.
And made me worse.
I dont really want to go, and I heard there a symptoms..
You know? Reasons to THINK you have it..
I dont want to worry my dad over nothing.