1st: why didn't you asparate? It's crazy important.
2nd: Why did you put a needle that was already inside you inside yourself again?
Bad form, use a new needle, lots of the needles have screw on needles, just toss the sharp part and screw another one onto the plunger if you REALLY wanted it.
3rd: You probably just nicked some sort of blood vessel. If you'd injected directly into the vessel you would be in a lot worse shape.
Pain is nature's way of telling you that you were an idiot.
Run through the procedures the right way next time man, I'm sure you know better.