One of the more reliable indicators of an infection is that the signs/symptoms progressively become more severe.
Many aas injections cause some minor redness/swelling/pain, but it is when these symptoms get worse and not better (eg. over 48hrs or so) that you are more likely to have an infection.
Read Junk's experience on his infection. The best thing to do is to go to your physician and have them possibly start antibiotics and drain the infection, if an abscess has formed. If you are shy about your aas use, just make up some bullshit story about sitting on a nail or metal shard etc.
If left untreated, intramuscular infections can progress to a variety of ends, including infection of bone (osteomyelitis), sepsis (bacteria in the bloodstream) and loss of the limb or even death.
Tholdren