Thanks for your query albeit short and specific.
The commonest cause of such a painful lump at the bottom of the spine is a Pilonidal Cyst. If it ruptured it is called a Pilonidal sinus.
The only sure-shot treatment is excision (total removal).
I would advise you to consult a General Surgeon for clinical evaluation, physical examination and investigations to get a plan for excision and cure. Please discuss with your treating Surgeon about the chance and percentage of recurrence as this condition is known to.
I hope this answers your query and helps in decision-making
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.