They seem like boils or furuncle. Boils are caused by infection of the hair follicle by staph aureus. Boil on buttocks is usually due to plugged sweat glands that become infected or by an ingrown hair.
Other possibility is of swollen lymph nodes or a sebaceous cyst.Lymphadenopathy (swollen lymph nodes) is usually caused by a viral or bacterial infection along with other numerous causes.Treatment is usually warm compresses,over the counter anti-inflammatory analgesics(pain killers) like acetaminophen or ibuprofen,antibiotics if cause of infection is suspected to be a bacteria and surgical drainage if there is any abscess formation.
Sebaceous cyst is a closed sac that fills with a fatty white, semi-solid material called sebum produced by sebaceous glands of the epidermis.It is usually painless but can become painful if infected.Then antibiotics are needed.
Apply warm compresses on the lump and keep the area clean.Drainage may be 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.
Hope it helps.Take care and pls do keep me posted if you have any additional queries.