What exactly are you allergic to? And what sort of injection was it?
I suffer from tree and grass pollen and had sever attacks all summer as a child.
Now, in my late 20's, I seem to get it for a few days in May, when a particular pollen is abundant.
Doctors seem to only prescribe injections to those who have a very specific, and indentifiable and easily treatable, reaction.
As it happens, my nose has been running a bit for the last few days, since the "heat wave" and the blossom is out in my neck of the woods (ha ha... oh the pun)