With the right antibiotic, chlamydia usually starts to clear within a few days, and most infections are gone within a week or two. The main thing is to avoid sex until treatment is finished, and until any partners have been treated, so you don’t pass it on or catch it again. Your doctor will give you specific timing advice, so follow that. Retesting after about 3 months is advised to exclude re-infection, which is common. However, if you develop symptoms in the meantime, earlier testing will usually be advised.