Night sweat prevention?

Is there a way to prevent this? It only started over the past couple months. It is every night. I wear a tshirt and underwear to bed. One night I even tried the nude. A thin sheet. The fan is on, the windows open with it being between 30-40 degrees out. I am sweating behind my neck, between my boobs and below, on my belly, in between thighs, and behind knees. It is so gross to wake up this way and it always seems to start early in the morning. I assume I am probably doomed til the end of my pregnancy.