Four Corners by Cassie Alexandra

Four Kingdoms.
No Heir.
An Uncertain Future.
After an evil curse is cast upon the four corners of Syracuse, a vast country ruled by the Rothhaven family, maidens across the land suddenly become barren.
Years pass and the future of Family Rothhaven looks bleak, until eighteen-year-old Mariselle Langer wakes up one morning with cramps, a craving for chocolate, and a highly unexpected visit from Aunt Flow.
Upon realizing that his daughter is menstruating, Mariselle’s father approaches the leaders of the four kingdoms with the wonderful news. This sets off a chain of events which threaten to divide the Rothhaven brothers, who all desire her for themselves.
Meanwhile, Mariselle has her own ideas about whom she wishes to wed, which not only shocks the nation, but ultimately… saves it.