My rectal chlamydia might be a resistant strain, still symptoms after 14 days, took 1000mg azithromycin. is there a test that doctor can use to find out which antibiotics it is resistant to?

Retest: Chlamydia is pretty responsive to Azithromycin. If you are still having symptoms, you need to be retested, and if necessary retreated. Make sure you are abstaining from intercourse for 2 weeks after treatment, and that your partner has been treated.

Yes, but...: This is not often done as chlamydia is hard to grow in culture. Often what is done it trying a second line antibiotic. More likely though is that something else is going on rather than resistance, so please be seen again.