I get this when I do not go deep enough after the needle comes out slightly in my shoulders (Find it hard to reach around these days!)
It is where you have not injected deep enough or have injected too quickly and the oil is sitting to high up in between skin and muscle.
I have done many a cycle and I am currently putting up with this on my right delt!
Dont worry, very rare for any infection etc if everything is swabbed.
So.. If you use an orange pin I wouldnt pin anything over 1ml with it... If you are getting it with 1ml then bump up to a 1 incher and inject more slowly.