I hope I am not being rude, but I think maybe the fear and anticipation is worse than the injection it's self.
How do you react when you do get an injection? It only takes a few seconds and the pain is usually not bad at all.
I understand the need to be in control and that horrible panicked feeling where you'd kill just to get away from the fear.
I do think if you watched people get injections it'd help, you'd see how they have no reaction and everything is ok, maybe then get a nurse to explain injections to you, show you the needle and how it all works and maybe with her
support work your way up to having injections with just the needle? Maybe even watch people get piercing done in tattoo shops? A lot of them are really friendly and don't mind you hanging around and asking questions