From what I learned in my research, yes I was diagnosed too and just finished my antibiotics course, that the bulls eye mark appears only in about 50% of the cases, and not always around the bite site itself either...
basically the bacteria gets into your blood stream and then can surface anywhere on the body. I actually had three marks, arm, leg and my side, hard to imagine that I was bit by three infected ticks at the same time, or that one tick traveled that far without falling off...
I had a habbit of getting the blood work for lyme test done twice a year, ironically i had blood drawn 2 days prior to the mark appearing, and it confirmed lyme.
they say that it takes 4-6 weeks fro it to show in the blood work after the infection, and that it takes 7-14 days for the bulls eye marks to appear. I guess it wasn't the case for me...
In addition to using tick repellants and checking for them post ride, i'd recommend getting blood test done two-three times a year, especially during summer, just to make sure you catch it soon, before any serious permanent damage had been done to your body. Lyme goes into all organs, liver, brain, etc... Untreated for long time, it will wreck serious permanent damage.
unfortunately, one does not gain immunity after the first infection and can be re-infected and the subsequent blood tests are alway false positive, I, and others who had it, cannot rely on them in the future and it's all symptomatic diagnosis from now on...
just my $0.02, YMMV
dz