It doesn't always hurt bit usually does. U might have hit the vein but came.out or pushed to fast. Always go slowly and check half way to make sure your still in fully and registering blood. Also give a you a change to access your tolerance and prevents od missed shots ect...it sucks getting to much blood in needle and having to surrender the rest of the shot but it's better then risking missing, blowing vein or shooting coagulated blood. Just toss it and booty rocket it,lol. For the swelling hot compress or towel and massage whatever is causing the swelling away from skin and back into body. Heat does wonders then I've for 30 to bring down inflammation. Should prevent any negative side effects of you happened to miss some of the shot which it seems u might have