What causes nausea right before a due period? Which hormones?

Prostaglandins. Most likely prostaglandins (pg, ) which are derivatives of arachidonic acid. Pg cause menstrual cramps, and can be associated with nausea, diarrhea, and mild temperature elevations - among other things. Pg rises dramatically before menstruation and peaks during your period. Otc drugs like Ibuprofen block pg; you might find it helps with your nausea.