I have tested negative for Chlamydia Antibody Blood test. Should I take the Urine NAAT test for it?

I have been tested negative for Chlamydia Antibody Blood Test after 3 months of exposure. 

During the last sexual activity my partner rimmed me as well. I am feeling itchy anus from last 25 days now ( 4 months after exposure) and hard stool too. Can it be rectal Chlamydia which was not diagnosed via Antibody test?

Anyone please help!