I took the one time dose of azithromicin 3 mos ago; i was still tested positive for chlamydia. why is this? what happened?

Rx fail, reinfection: This isn't rare. 5-10% of people with chlamydia have new positive tests after 3-6 months. That's why retesting is recommended. Either you are reinfected (if sexually active and potentially exposed) or treatment failed, which happens 2-3% of the time with azithromycin. Your current partner(s) need to be tested and treated, and you need re-treatment, probably with doxycycline, not azithro.

Uncertain: Did you completely abstain from having sex for at least 7 days after treatment? Having continued sexual relations with someone who has Chlamydia can be a reason or you may simply have been re-infected by someone since then.