Hi, Thanks for writing to us. Firstly let me give you a clear understanding of few terms , Fistula is a tract that connects two structures that normally do not connect. So a fistula can form between urinary bladder and intestine or bladder and vagina etc. Another term is sinus. A sinus is a tract that just drains fluid. Sometimes when sebaceous cyst are not excised in toto along with their epithelium lining, chsnces of recurrence are very high. Same could have happened in your case. Bikini area is area prone to sweat and moisture and so the lesions might not have healed properly. If that is the case, use antibacterial soap for bathing. Do warm water compresses in the area followed by antibacterial cream application. Also take a course of oral antibiotic for 7 to 10 days. Thid would help in settling the infection if any. Also meet your surgeon again for follow up and examination of your existing cyst