Rather than suggesting an abx that you "should" use, as this varies for each person depending on so many different factors, here are some articles that you can read to better understand what the purpose is and how to combat cystic forms:
www.lymeinfo.net/lymefiles.html This is a link to the first article on cyst forms in LD, and the best place to start in my opinion:
www.lymeinfo.net/medical/LDCysts.pdf There is ton of information on these pages, for both the "beginner" and the more "advanced" reader. Please take the time to educate yourself, then you can talk with your doctor better to find out what is right for you.