Unfortunately, Lyne isn't that easy to catch. That's one of the reasons I believe I'm in this boat. The testing is inaccurate and the controversy over the disease has gotten very politicized. I tested negative 7 times over the years. I believe I was bitten 2007 of earlier, but it's hard to say.
Unfortunately, the spinal tap may not be definitive either. I've had two... Neither led to my diagnosis of Lyme. I found a savvy infectious disease doc who knew how inaccurate the tests are, and started me on antibiotics. It wasn't until then that I knew I was on the right track.
And honestly, I'm not big on putting stuff in my body either. To me, antibiotics were a better choice than the current choices for MS. I strongly suggest joining a few other groups online if you have the time, Yahoo offers some great Lyme forums and MS have a great site called This is MS. There are a bunch of supportive folks out there who can help guide you throu this process. Finding a doc to give you antibiotics will be a challenge. According to the CDC, late stage Lyme is rare. Docs follow that, and will dismiss you quicker than not. I had to find my specialist through one of the Lyme support groups on Yahoo.
I do caution you in this regard though.. Trust your gut. People on both sides of the Lyme/MS club tend to sway you in one direction or another. These past three years have been nothing short of a roller coaster ride for me between these two diagnosises. But you'll make it through.. The beginning is the scariest, so make sure you have a good support system. And if you don't, try to find one online.
I hope you find your answers.