I had been treated for chlamydia almost 3 weeks ago and i still sometimes have discharge. could i still have the infection?

Not chlamydia see MD: With the standard treatments (azithromycin 1 gram, single dose, or doxycycline twice daily for 7 days), taken as recommended, and not reexposed, it is almost impossible you still have chlamydia. It can take 1-2 weeks for symptoms to clear, but 3 weeks is too long. Re-check with your doctor about evaluation for other causes, like gonorrhea, trichomonas, bacterial vaginosis, or yeast.

Yes,possible: If infection is treated and there is no exposure,it is unlikely that you have infection,it could be normal discharge,observe,if persist may get retested for both GC and chamydia.Both partner should be tested.