What makes me me?

I have been thinking a lot lately about what makes me me.  I know the standard church stuff, I am an eternal being and I lived before I came to earth and I will live after and I am a child of God, but what makes me act the way I do and make the choices I do?

I believe that what I have learned through church and school and experiences plays a big part in the way I act and the things I do, I believe I have an eternal spirit, but how much of who I am can I really change?

I know that through God all things are possible, but are they all possible for me?  Is it possible for me to stay calm and not get overwhelmed when I have a million things coming at me?  I have learned tools to help, but I don't seem to be able to remember them in the heat of the moment.  Other people can, they stay totally calm in any situation, not me.  I get hyper, I know because my coworkers tease me about it, some of them laugh,  I can tell others get really irritated by it, it doesn't mean I don't solve problems and deal with things appropriately because I do.  It does mean that I sometimes irritate or offend people in the process, neither of which is a very desirable outcome when in a stressful situation and wtih people I have to deal with all the time.  So I apologize...a lot.

My question is can I change that, and if I can, should I , or is it part of what makes me me and if I change it I won't be me any more?  Would I be better off to just accept that I get hyper, that's just me, and figure out ways to use that to my advantage or should I keep working hard to change myself?  Maybe I should keep working hard to change myself, but my efforts would be more effective in another area, like developing more patience or being more positive, maybe I could actually make progress in those areas?   

I don't know, a lot of this probably doesn't even make sense when you try to read it.  One would think that by the age of 47 I would have these things all figured out, apparently not because right now I pretty much just have a lot of questions.   Anyone have a good answer for me?