Lyme diagnosis can be difficult. Lyme can often occur along with other diseases and can be mimicked by other disease, for this reason, a concrete immediate Lyme diagnosis can be tricky.
A physical exam and time spent talking with your doctor is usually the first steps. A typical rash only occurs in approximately 30% of individuals. The hallmark "bullseye rash" most notoriously associated with Lyme occurs in less than 15% of patients; so the lack of either is not necessarily a non-diagnosis.