If you had an infection it would most likely be staph or strep based as they're the most common that tend to be carried on human skin. If you were clean and used a reliable lab it's unlikely that you got said infection.
I've only been pinning myself for 6 months now mostly for TRT and a little boost hit and miss and what I have noticed is that there is so many factors that play into PIP and swelling. It can depend on the site or how much you move like a few guys mentioned, using a larger then needed pin, but then comes the chemical level. Some guys are more sensitive to the preservative BA more then others, said guys will always have more PIP, then the concentration of your gear matters, which ester plays a roll as well and even down to what oil is used to produce it. You will notice in time the PIP will decrease but if you change up labs and they're mix is different you may notice the PIP return because of the composition of the new lab.
I'm hyper sensitive to PIP and I get swollen knots at times and they do get warm, even at times I can feel a little off or achey like it's making me sick but no abscess ever pops up, and I've have some gnarly PIP knots, the swelling down to the knee also happens to me... current product I'm using seems to disagree with my body so will be tossing that and going back to the PSL. I will say the synthetic oil PSL uses is epic for sensitive individuals like me, it will be 100% clear test and that stuff doesn't bother me at all. Currently trying to find out what the brown vials are brewed with.
The mildest stuff I have ever used had been a test-cyp that was made using grape seed oil, I cannot name manufacture due to rules but I would suspect anyone sensitive to any enenthanate lab they use them to try cypionate.
Sorry to rant.. just including my personal experience and what I've discovered in my adventures this far. The thing I mentioned about PSL test (the clear batch, synthetic oil) isn't a choice... I've received many more brown ones then clear. In fact I have yet to use a brown one, I ran thru the clear first and my pharmacy Watson, then the new UGL test-e that's kicking my ass.... like I mentioned above not virgin muscles anymore and it makes me feel rough at a mild 1ml a week (250mg) a week.
So to sum it up this could possibly never end based on the product you're using if you're body is sensitive, but it's normal and to be expected when first pinning, of it persists please try PSL gear or drop the extra cash to get some pharmacy grade cyp, also find cyp to be more mild then eth... read many guys say the same on here.
If an infection indeed is brewing you will know when it happens, as I have had one based on a shot a nurse gave me that some how got messed up. If it is infected it will continue to get worse day by day then literally hour by hour, and if untreated can lead to septic shock and necrotizing fasciitis if untreated. You would notice feeling ill, aches in your lower back and thighs like no other, fever, common flu symptoms, random unexplained fever. If you watch the sites you will likely be able to tell this is happening before it turns system wide like I'm talking about, you will notice the pain getting worse and the type of swelling change, more area of the leg may hurt like spreading down the entire leg its self, and it will become extremely red and angry looking at the injection site/around it, the heat will increase to the point that it's literally hot hot.. not just a little warmth from regular PIP.
Again sorry for the long post but make no qualms about it, bacterial skin infections are not a joke and certain forms of them can become more common after the first infection. The only way to know what bacterium caused the infection is a biopsy, most would agree that MRSA (resistant staph, standard antibiotics won't help at all - meaning anything from the penicillin family including cephalosporins) is the worst case scenario and many people get repeat episodes, then comes the non-resistant staph and strep which respond well to most antibiotics especially stronger orals like clindamycin. Bactrim can be useful for MRSA but it isn't the first choice for serious infections, vancomycin is the goto drug and it's IV. Apparently from the research I've done lately there has been reports of MRSA morphing more and becoming resistant to vanco... it's scary how fast it happens. A few years back clindamycin could be used to treat MRSA easily but it grew resistant to that. Anyway this isn't to scare you I just love science and have suffered from various types of bacterial infections that have nearly taken my life... thankfully not MSRA but I've have had repeat outbreaks of strep and staph included cellulitis and it sucks, I have went septic and suffered the necrotizing fasciitis. And yes I'm clean and keep a super clean house so I'll explain another time why this is... believe it or not it's easier than you think.
Last apology lol, I just love science and really take an interest to microbiology. Don't run out and jump on antibiotics for no reason either, you don't want to use them unless it's completely necessary because they will indeed lose their effectiveness in you eventually.