I'm sorry you have had continuing complications from LEEP. I did, too. LEEP, unfortunately, has the highest risk of infection, so I get irked when anyone tries to play that down.
The vitamins to take for boosting immunity are vitamin C, beta-carotene, and folate. But going to a professional who can work with you on supplements, etc., would be the best option because that person can tailor the "menu" to your needs. I found an accupuncturist/herbologist who has developed a vitamin/herb supplement program for me that I swear by. After six months, I was finally able to sit down without pain killers and a cushion. I still have to get up and walk, at the end of a work day, or the area still aches a bit. But that is tremendous progress, in my book. I wish I had sought integrative medicine sooner, now.