Hello,
Welcome to the ehealthforum and I am really glad to help you out.
Your concern is regarding the painful bump that you have on the butt crack. Indeed, the symptoms are suggestive of a pilonidal cyst. It 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.
My sincere advice would be to get it examined by a surgeon.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are advised to consult your doctor. I sincerely hope that helps. Take care.