What Causes Nausea And Vomiting During A Menstrual Period?

Hi, I took Levonelle 2 weeks ago on day 9 of my cycle. All was ok for a week then I had a light brown bleed with clots that I assumed was early period. 2 days later I bled again and still am, more normal period blood with clots but had terrible nausea on the edge of vomiting last night. Is this coincidence or has something gone wrong here?