I am a healthy almost 38yo female, 5"4, 119 lbs. I was just given Metoprolol Tartrate for high blood pressure. What could be causing this? Family history?

Possibly . However most of the time there is no clear cause or association for having a high blood pressure, good that you started controlling it, kindly keep taking your medicines, check your eye pressure too, maintain your healthy lifestyle and keep the follow-up with your doctor, best wishes .