He's probably using not Mex Sustanon, but one that comes in ampules.
Transporter, what brand exactly are you using? Also, what is lot # and expiration date?
Have you reused any needles? how about the injection area? did you clean it before hand?
Don't feel bad if you reused needles... I have done it before since they are so danr hard to get in my State
It truly sound like an infection.... I have had something like this before and got rid of it with by taking some AntiBiotics.... a shot and some oral dosages, but I caught it way early... if it has progressed past that point... they might have to cut it open and drain the puss.
You might need to go to the doc... He will lecture you about your AS use, but fuck it. Nothing more you can do. He'll prescribe some AntiBiotics or if you are past that point you'll get it drained like I posted earlyer.