Two days after finishing a seven day doxycycline course on chlamydia, I took another test with positive result, how long it takes to clear completely?

Chlamydia retesting. You were tested too soon. Doxycycline never fails to cure chlamydia, if taken as directed. However, even though chlamydia is killed by the antibiotic, its DNA takes a while to clear -- and the test detects DNA. Chlamydia retesting is not recommended until at least 3 weeks aftertreatment. In then, it's usually unnecessary. The most important time for retesting is 3-6 months, in case of reinfection.