People get different reactions from injecting. If it seems to be getting better, you are probably okay. If it doesnt go away, I would recommend going to see a doc.
The below is compliments of partyboy:
Firstly you need to distinguish between a septic and sterile abscess.
If its septic then antibiotics are useful in the early stages.
Different antibiotics are active against different bacteria.
Different abscesses (depending where located) need different antibiotics.
Commonest causes of skin abscesses are Streptococcus and Staphylococcus aureus.
In hospital when I was working in Surgery we would usually use a combination of Flucoxacillin and Penicillin.
Augmentin alone is also effective. Note: augmentin is Co-amoxiclav (Amoxicillin and clauvinic acid), which makes it different to just amoxicillin.
Dose 250mg three times a day (up to 500mg three times a day if serious).
Cephradine can also be used but there are newer and better cephalosporins.
However, antibiotics are useless in the treatment of a well-established abscess because they can’t reach the contents, so if you have an established abscess you will need treatment.
An abscess is a localized collection of pus in any part of the body, usually caused by an infection. Abscesses occur when an area of tissue becomes infected and the body is able to "wall off" the infection to keep it from spreading. During this process "pus" forms, which is an accumulation of fluid, living and dead white blood cells, dead tissue, and bacteria or other foreign invaders or materials.
The majority of abscesses are septic (ie caused by an infection) but sterile abscesses can also occur which are not caused by germs but by non-living irritants such as drugs. If an injected drug, especially oil based ones such as many anabolic steroids are fully not absorbed, it stays where it was injected and may cause enough irritation to generate a sterile abscess. Sterile abscesses are quite likely to turn into hard, solid lumps as they scar, rather than remaining pockets of pus.
(Superficial abscesses are readily visible and are red, swollen, painful and warm. Abscesses in other areas of the body may not be obvious and may produce only generalized symptoms such as fever and discomfort. A sterile abscess may cause only a painful lump deep in the buttock where a shot was given.
If the abscess is small (less than 1 cm or less than a half-inch across), applying warm compresses to the area for about 30 minutes 4 times daily can help.Additionally, localized warm/hot soaks three to five times daily frequently brings an abscess to heal.
A culture or examination of any drainage from the lesion may help identify what organism is causing it. Most will continue to get worse without care. The infection can spread to the tissues under the skin and even into the bloodstream, resulting in septicaemia which can be very serious. Unlike other infections, antibiotics alone will not cure a mature abscess. In general an abscess must open and drain in order for it to improve. Sometimes draining occurs on its own, but generally it must be cut open by a doctor in a procedure called incision and drainage.
Once the sore has drained, the doctor will insert some packing into the remaining cavity to minimize any bleeding and keep it open for a day or two.