Don't know the answer to the questions specifically. I'm going to assume sometimes you get sworness and redness and other times you don't and can't quite figure it out. Well the same thing happens to me. I've got serious pain in my left thigh as I type and I did a shot of the same volume from the same bottle, (different location)a few days before that with absolutely nothing by way of pain or swelling or redness. I guess it's just a roll of the dice sometimes. Don't know if this helps, if not sorry.