I Have A 12 Week Old Infant. I'm Breastfeeding And

I have a 12 week old infant. I'm breastfeeding and supplementing. My husband and I had sex 5 days ago at like 4am, and the same morning around about 9 took the plan b pill. Well, about a day ago I experienced some nausea. Tonight I had bright red blood on the toilet paper when I wiped.. when I urinated again a little later, there was no blood. Are these plan b side effects or...????