I'm 5wks Postpartum, I Had Sex With A Condom But

I'm 5wks postpartum, I had sex with a condom but it broke we were still careful. I also took a plan b one step 48hours later. I had some cramping and brownish discharge 3days later. I'm not breast feeding. Any advice? Not sure when I'm suppose to start my next period, so I'm wondering when I can take a test that will be accurate?