If you hit a vein it's very unlikely to kill you, but most people indicate it's a bad and painful experience including respiratory problems similar to what you're mentioning. If this is related to the injection it will pass and symptoms should be getting less by now. I'd be more worried if it's NOT related to the injection. Then you're looking at a real potential health threat. Do you have any other symptoms?
Chest discomfort. Most heart attacks involve discomfort in the center of the chest that lasts more than a few minutes, or that goes away and comes back. It can feel like uncomfortable pressure, squeezing, fullness or pain.
Discomfort in other areas of the upper body. Symptoms can include pain or discomfort in one or both arms, the back, neck, jaw or stomach.
Shortness of breath. May occur with or without chest discomfort.
Other signs: These may include breaking out in a cold sweat, nausea or lightheadedness
If so, don't respond to this thread. Get the fuck off the keyboard and go to the ER.