Can a doctor tell if I've had chlamydia? I don't want to tell I've had it in the past.

No, a doctor can't tell by visual exam, but it is in your best interests to give the doctor your complete medical history including any STDs you have had.

There is no reason to be embarrassed, many women have this. Also, if it was left untreated for a while it could have caused problems with your reproductive health.