What Causes Slow Healing Of Wound Post Surgical Removal Of Pilonidal Cyst?

Hi Doctor, I am a 31-year-old man who had surgery for a non-healing pilonidal cyst wound about 3 1/2 weeks ago. It was my third surgery in the area: the first was in 2002, which healed successfully, and the second was last March (2014), which never fully healed. The surgical wound is healing very slowly, and my doctor said it is "highly unusual" to not be more advanced in the healing by this time. I am concerned about potential underlying causes for this slow healing. They have taken a biopsy and I am awaiting the results. I do not have any symptoms of diseases like diabetes or Crohn's. By all appearances, I am healthy--before the surgery, I exercised a few times a week, had a generally healthy diet, and although on occasion I drink too much, I do so far less often now than I did in my 20's. My blood pressure is in the upper normal range. I am taking an antibiotic, Bactrim, in case the cause is MRSA. My one concern is that the underlying cause of the slow healing, if there is one, could be related to my sexual history. I have had sexual encounters with some high-risk persons, and while I practice safe sex almost always, I don't want to rule out the possibility of an accident that resulted in transmission of a disease. Given this information, do you have an idea of what the cause of the slow healing could be?