I also find it very hard to beleive the doc allowed you to self medicate.
The Deltoid muscles can only cope with small IM injections of substances. Most oily preperations take longer to disapate in the tissue. Usually anything over 2-3ml is put into the gluts or quads.
You need to know what you are doing, when anministering injections, infections, hitting bones, damaging nerves hitting arteries etc, are all possible unless you have a decent anatomical knowledge. You hit a nerve it hurts like crap and you may loose use of that limb for a short period or permanantly.
But being that the deca is only being used to treat an injury I am supprised you would have any issues and the doses would probably be quite small, and a week or more apart..
Edit just saw the other post,...
3 months you are a nut to inject yourself for 3 months with out proper instructions. no wonder you have sore shoulders, I bet you have created scar tissue in there by pounding the samespot over again...are you alternating shoulders?
It is Ok but The doc you got the drugs from should be able to surgically remove any scar tissue ( wont help your mass gain however). Also any damage you have caused will effect every injection you get there for the rest of your life, scar tissue does not allow penetration like muscle fibres
Yes I have been taught how to inject, but mostly remove blood from patients.
Go see you "doc" and get better advice, or go get a second opinion.