needles in the freezer? Whoever told you that, fill a syringe full of air and inject their carotid artery with it. Total bull.
Did you move the pin around alot while it was in your ass? Did you inject the upper, outer quadrant of your buttcheek? Warming the vial will help some, but i wouldnt go warming amps, they may pop. Better off injecting smoothly, and then massaging the injection site afterwards. It also helps if you inject an area you are about to go to the gym and hit, asd it moves the oil daround. works for me at least (if i were to inject, which lord knows i woul dnever do).
also, if you are inecting sustanon, chances are it is gonna leave you sore. high Ba content, and it has prop in it. Sorry, but thats the deal with that stuff.