This type of lump on coccyx can be a boil or a pilonidal cyst. Pilonidal cyst is a cyst right over the coccyx
area. In this the skin becomes reddened or even sometimes looks like a small bruise. When it is infected, it
causes pain. Antibiotics or surgical drainage may be required. Boils are caused by infection of the hair
follicle by staph aureus. Apply warm compresses on the boil and keep the area clean.Drainage of the boil is
done only when it becomes soft and forms a head.Take some over the counter pain reliever and consult a doctor
for examination and antibiotics prescription. I hope it helps. Take care and regards.