It may be a boil or carbunkle, you should read the information below.
Sit in a hot bathtub regularly to draw the boil/carbunkle out. Use ozonol on it! and it should pop on its own.
http://www.bing.com/health/article/mayo-126164/Boils-and-carbuncles?q=boils
Symptoms
Click to enlarge
A boil is a painful, pus-filled bump under your skin — the result of a bacterial infection of one or more hair follicles.
BoilClick to enlarge
A carbuncle is a cluster of boils — painful, pus-filled bumps — that form a connected area of infection under the skin.
CarbuncleBoils
Boils can occur anywhere on your skin, but appear mainly on your face, neck, armpits, buttocks or thighs — hair-bearing areas where you're most likely to sweat or experience friction. Signs and symptoms of a boil usually include:
A painful, red bump that starts out about the size of a pea
Red, swollen skin around the bump
An increase in the size of the bump over a few days as it fills with pus (can sometimes reach the size of a golf ball)
Development of a yellow-white tip that eventually ruptures and allows the pus to drain out.
Once the boil drains, the pain usually subsides. Small boils usually heal without scarring, but a large boil may leave a scar.
Carbuncles
A carbuncle is a cluster of boils that often occurs on the back of the neck, shoulders or thighs. Carbuncles:
Cause a deeper and more severe infection than single boils do
Develop and heal more slowly than single boils do
Are likely to leave a scar
Signs and symptoms that may accompany carbuncles include:
Feeling unwell in general
Fever
Chills
When to see a doctor
You usually can care for a single, small boil yourself. But see your doctor if you have:
A boil on your face or spine
A boil that worsens rapidly or is extremely painful
Boils that are very large, haven't healed in two weeks or are accompanied by a fever
Frequent boils
A condition that suppresses your immune system, such as an organ transplant, corticosteroid use or an HIV infection
Recently been hospitalized
Children and older adults who develop one or more boils also should receive medical care.
http://www.medicinenet.com/boils/article.htm
http://www.bettermedicine.com/article/carbuncle/causes