What the f*** is my problem?

As long as I can remember I have had this "problem", I get so freaked out by certain situations, that nothing can calm me down, reassure me, absolutely nothing, not a supportive friend,not anxiety medication,no meditation, nothing helps. I just totally loose it, I can't sleep for days before it, I can't think about anything else but that upcoming event and I hate myself for being that way. Because somewhere deep down I know it's stupid, and I am easily capable of doing what needs to be done, but I can't pull that belief to the surface, no way, no how. Then once everything is over, I wonder what my problem was, because everything just went great, I knew I was gonna accomplish it, so what was the big deal about it? One would think that with everything I accomplish my confidence muscle would grow or at least stay at that level, but as soon as the next "test" comes along I will freak out again. It just drives me crazy, because in the end all this anxiety was for nothing, lost sleep for nothing really. I always tell myself the next time I won't get stressed out like this, but it never happens.