What does Caffine do to you?

I quite drinking caffine like a year and a half ago when I got preggie and have stayed off it cuz of my anxiety. Now I get crazy gitter when I have caffine. Almost like I took a couple nodoze. I feel all wacked and crap! Is that the caffine or a psychosamatic(sp?) thing cuz I know caffine does not sit well now? Like I know part of it is the caffine! I am so used to not having it my body doesnt like it. But could it partly be psychosamitic? I dunno I know I feel better without it.
Does caffine affect you weird??