Chlamydia false positive?

Raven.
My fiancé and I have been together for 4 years and have been extremely faithful with each other and still have had annual STD checks. 
I'm 4 1/2 months pregnant, got tested for STDs a month ago and the doctor just called and said I tested positive for chlamydia but we have both been clean for years. I asked if they could retest and another nurse said "absolutely not!" and that I should take the medication. 
Neither of us have shown symptoms of any kind whatsoever. 
Is it possible it's a false positive and her waiting a month to tell me..that the lab got results mixed up with someone else's? Please help. 

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