Erythromycin for chlamydia while pregnant?

So my MW checked me for STD's back in march, & I had chlamydia which was from my sons father whom I no longer am sleeping with after that. They gave me this one medicine (forgot the name) & it was 4 small pink pills I had to take all at once, so it was an easy treatment. They re-tested me again, and my results come back positive for chlamydia.. I am currently 31 weeks pregnant, and I just am worried that it won't go away. I have NOT had sexual intercourse since I last slept with my sons father, which was over 3 months ago. I am currently taking erythromycin which is considred safe during pregnancy. I have to take 4 pills once a day for a whole week, so it's a more sucky treatment. I am worried it won't go away, & if it doesn't will I have to get a c-section or what will they do if it doesn't go away?