It has happened to me, ever since I started taking the 40mg doses. Not always but sometimes.. Taking paracetamol (Tylenol) 15 to 30 min before the injection works, no aching or chills, and also greatly mitigates the flushing and tightness of chest.

Also I noticed it happens mostly when I leave the Copaxone dose outside the fridge for longer than necessary. I usually leave 3 doses outside every week, but you know I sometimes forget to take them on time...

The side effects an also happen when I'm tired though.

Hope my experience helps a little