C6 elisa is very sensitive, well... not "very" but better than other stock lyme elisa tests for sure.
yes symptoms creep back in. are u generally sick for longer than 6m? if u caught it very early (first months) then doxy may be all u need. many ppl here were not so lucky.
doxy for early lyme is ok, but the good dosage is 200mg twice daily/www.tandfonline.com/doi/full/10.1586/14787210.2014.940900