I am sorry about that I know it is hard especially when you are so young. Ok, your stepsister has bipolar doesn't necessarily mean that you. Mental Illnesses can have a higher incidences of being passed in the same family. However, there are plenty of people that don't have a family history of any mental illness that still are diagnosed. Depression with manic features meaning you would have really high days then experience really low depressive states is bipolar. A more extreme state of bipolar disorder is schizoaffective disorder which is completely different from schizophrenia. There is strict criteria that has to be met and evaluated by a psychiatrist before you are diagnosed with anything of this nature.
My brother has Bipolar Disorder and Explosive Personality Disorder however, I have Major Depression and Post Traumatic Stress Disorder. So just because my brother has BP doesn't mean that I will have it or develop it.
So have you taken all of those medications you listed since you graduated 6 months ago? I would have some concerns that the doctor didn't give them enuf time to work. Some antidepressants have to reach what is called a "therapeutic level" in your body which can take weeks.