When pinning eod its always good to work on your 6 site rotation, sounds like you are mainly pinnng delts, you are going to get a buildup of scar tissue if you don't rotate to glutes and quads etc.. less painful in the long run as well.... The spots could be acne, my.acne on prop was different than what I got when I was a teenager, or it could be from your pins, do you change tips after you draw the prop into the syrenge?(spelling) depending on the brand of needle, it can dull the needle quite a bit going through the stopper.... I use an 18 gauge to pull and 23 to inject.