I think I have chlamydia. Which antibiotics can I buy to cure it...?

Azithro, doxy. You're in Ukraine, right? Get professionally evaluated if possible. Chlamydia, nongonococcal urethritis (NGU), and to some extent gonorrhea cause similar symptoms, and gonorrhea requires different treatment. The main treatments for chlamydia and NGU are azithromycin 1 gram, single dose; or doxycycline (or another tetracycline) for 7 days.
Doxycycline. Chlamydia is usually treated with Doxycycline 100mg twice a day for 14 days. It can also be treated with a single dose of Zithromax (1000mg). Doxycycline should not be used during pregnancy. Best wishes!