What Causes Nausea And Spotting After Intake Of Plan B?

I took plan b on Saturday, had some minor nausea, and then felt fine. It's 4 days later and I feel very sick now. Haven't been able to eat normally, and I'm spotting. I know the spotting is connected to the plan b, but what about the sudden nausea that came on Tuesday night? Is that a stomach virus separate from the plan b side effects?