Did stress cause me to lose my last pregnancy midterm?

No. The most common cause of pregnancy loss in the second trimester is a problem with the structure of the uterus. If you have a septum or congenital anomaly of the uterus (uterus divided into two horns), these structural problems can put at risk of prematurely losing a pregnancy. Any prior surgery of instrumentation on your cervix or placental problems can also increase your risk of miscarriage.
Don't know. There is no way to answer your questions. There are too many possible reasons for losing a pregnancy to pick just one, particularly since i'm not your physician. Ask your ob, they may have more information.