post partum pregnancy risk

Hi
I had sex 5 weeks post partum(yesterday). My husband did not ejaculate- altho I am not silly enough to think that is adequate contraception!
Anyway, I have now a stringy mucous discharge (not unlike when one ovulates). My main concern is that I am due to have an IUD inserted in a week.
Would a progesterone blood level indicate if I had ovulated this soon after delivery or would my level be high anyway? I also have a MAYBEBABY saliva microscope which indicates ovulation but is it valid now?
How soon would BHCG levels show if I am pregnant.
I expressed milk only twice a day for 4.5 weeks for my baby until I could not supply enough for his needs.
Advice would be appreciated.
Thanks