I have pelvic pain even after chlamydia treatment. could i have had pid? or is it a side effect of chlamydia?

Possible: You should be checked to make sure the infection is gone.

Yes: Yes to both. It can be hard to diagnose pid, but pain afterwards can be caused by pid. In some cases it can progress to become a chronic problem. I think you should be seen to have a more thorough evaluation, and to make sure that the chlamydia infection responded (was cured) by the treatment, b/c if it is still present, then your chance of having chronic pain increases (infertility, too).