Have you seen a psychiatrist so that you are sure that depression is your correct diagnosis?  I know mental illness does run strong in families, so there is a chance you might have bi polar, but please find a psychiatrist to be properly diagnosed.  It's not good to diagnose yourself, that could lead to bad things.  Are you on meds for depression?  And if so, what doctor do you get those from?  Only a psychiatrist can properly diagnose you and medicate you.  I'm not sure of the exact chances of you having the disease, but that really doesn't matter.  You need to find a doctor.  Have all of your family members been diagnosed by a psychiatrist?  And do they see one on a regular basis?  If you are that worried, please find a doctor for a diagnosis.   Good luck!