Hi Cheri21157,
This topic has come up a few times recently. I'm not sure what the bottom line is, but you can find a recent thread with different ideas/experiences here:
http://www.medhelp.org/posts/Lyme-Disease/Antobiotics-affecting-test-results/show/943269
I can only speak from my experiences, and i believe i read somewhere you should be abx free for at least 2 weeks, so i went 2 months with none.
I wanted to make sure there were none in my system, so the test had a chance to test pos, and it did...see my testing here.
http://www.illinoislyme.com/Test_Results.htm
scroll all the way down past the explainations....hope this helps you.