So I've been taking 500/mg Test C a week, pinning twice a week for 6 weeks now. On my last pin, I pinned on a Thursday - by Friday morning I had noticed I had started to develop what appeared to be hives on my elbows and on my lats underneath my arm. I took an antihistamine and didn't think much of it. By Sunday morning these hives/rash had begun to really spread and was starting to turn a bright red and have small bumps. At this point my entire body had felt pretty itchy and had spread all the way throughout my body, bulking up specifically in what would be considered "hot spots" so arm pits, backs of knees. I decided to head to urgent care - where they have a shared file of my medical record. My doctor has been aware that I am on gear and helps me get my blood work done regularly. While at Urgent care, the doctor that was handling me told me I had basically a subcutaneous skin infection - that was most likely due to a sharp decline in my immune system from gear. While, I had figured this was most likely due to the gear I've been trying to pin point down a reason this could've occurred to prevent this from happening again.
The Reasons I've thought of are:
- Switched vial on the pin previous, possible different/bad batch?
- First time using test c, possibly allergic to oil base?
- Not sterile pinning practice (I've always been very careful about this, but I don't want to rule anything out)
- Immune System Decline (Never Heard Of This, but not sure)

I was prescribed Antibiotics which started to reverse the effects within a day, so I'd imagine this was some sort of infection. Has anyone had a similar experience or can provide some sort of insight so I can prevent this from reoccuring. The doc recommended I tapered off and never returned to gear again, go figure - but this was something I found relatively concerning.
Thanks for the help in advance!