I have studied your case and I think you are having Pilonidal sinus. This condition is common in hairy people and it causes pus accumulation in side a sinus. It occurs when person is obese, sits for long time on the stool. It causes hairs to enter in the skin and pus forms. I would recommend you to show it to general surgeon and he might start you on oral antibiotics. If these antibiotics will take care of pus than it is better otherwise you will need a small surgery. In this whole sinus is excised and than it is left open so slowly whole sinus heals. You might need daily dressing. For future precaution you should loose some weight and should not sit for long time. I hope this answer will be useful for you. Let me know if there is any other followup questions. Thanks.