I have a bubble imbetween my buttcheek what could it be?

Pilonidal cyst. You may have a pilonidal cyst. A pilonidal cyst is a cyst that develops along the tailbone (coccyx) near the cleft of the buttocks, approximately 5 cm from the anus. These cysts usually contain hair and skin debris. Individuals with a pilonidal cyst may not have any symptoms at all (termed asymptomatic), whereas others may develop an infection of the cyst with associated pain.
Pilonidal sinus. If the "bubble" has persisted for more than a week, it is time to see a doctor. It could be from friction between the "cheeks" which may get agravated by hair lodging in the wound. The "bubble" could get infected and become a chronic ulcer.