You can't just dismiss a diagnosis over one symptom; not sure if temper tantrums really have anything to do w/ bipolar. From what I've been told...bipolar tends not to even be diagnosed til later in life....you need to have some history established...it's pretty complex to accurately diagnose. And having said that, I'm not trying to say that no adolescense are ever diagnosed or that the ones out there that have been diagnosed are that out there w/ incorrect diagnosis hanging over their heads.
As well as you can't dismiss something so quick based on one symptom...you shouldn't rush to assume that you are dealing w/ something based on one symptom. There are SEVERAL factors taken into consideration when a dr. gives a diagnosis. A person can have many symptoms of a particular something but at the same time not be dealing w/ that due to other factors only a professional can understand and take into account.
As you can see...I'm a big advocate when it comes to NOT trying to self diagnose.
I honestly believe...at least from how you post lately and the things you write about....now mind you I"M NO PROFESSIONAL...just my take on things from where I've been.....BUT....my suggestion is to stop stressing that you are going to walk in to a counselor's office and walk out w/ some big label hanging over your head. I honestly believe that it's most likely that you are dealing w/ some very normal "stresses" that can happen at your age. But that unfortunatly for you, you are not as equipped as some people are in trying to handle that much of a load or begin to understand it. I bet if you had, first of all; less of a load to deal w/...and second of all....a better understanding of how to manage it all and deal w/ the stresses....I would bet you'd do a lot better then you feel you are now. It's truly not uncommon to feel stressed at your age w/ the type of load you carry. And it's certainly not uncommon to have these issues weigh on you heavy enough that you start to feel depression on some level...frustration...weighted down by the world. You'd be shocked to know just how common that is. But again...that doesn't mean you are good at handling it! That's the key...AGIAN IN MY OPINION!!!....that you learn how to balance the load you have....maybe even learn areas you can cut back a little so things don't seem so overwhelming to you all the time.
Just my opinions! Again I remind in excess...I'm not a professional. I've been through a lot though and so from that....this is where my opinion comes from. You can take that as it is offerred up