Cephalexin should not make a dog's ears so clean that there is no wax. You may just be lucky so far. How long was she on the Cephalexin?
Cephalexin can make a dog's stool loose due to the lack of healthy flora in the gut. It just depends upon the individual dog and their tolerance for this antibiotic.
Doxycycline is the usual drug of choice for Lyme disease.
Sabra - female GSD - born April 30, 2012
Sargeant - rescued senior GSD male/foster failure - approximately ten years old (August 2013)
Max - rescued GSD - Dec 22, 2010 to March 7, 2012 - at the bridge
Sable - rescued GSD - at the bridge