Ask your health care provider. Generally, it will be safe to have sex one week after both you and your partner have completed the entire duration of antibiotic treatments, provided all symptoms have disappeared. It is possible to get chlamydia again immediately after your infection has been cured.
Remember, your recent sexual partner(s) have to be tested, and if they are also infected, you will need to wait until they have finished treatment and been completely cured before having sex.
It is always a good idea to use condoms to prevent STIs, but they are particularly important after you or a partner has been treated for an STI.