Evening primrose oil

Has anyone ever used evening primrose oil to ripen your cervix? I read that you can insert the capsules vaginally or take them orally. I took one 1000mg orally yesterday and started having back contractions so bad I had to lay down. It could have been completely unrelated to taking the primrose supplement, but I haven't taken anymore bc I'm only 35 wks. I have also started drinking red raspberry leaf tea this week to help strengthen my uterus for labor.