My sex drive was off the charts during all four of my pregnancies, specifically during the third trimester. The hormone changes can work either way. They can make her really, really horny or completely deplete her sex drive.

My OB/GYN recommended sex and walking to induce labor the closer I got to delivery. Unless your wife's doctor thinks it's a bad idea for her to give birth this soon and tells you to chill out so she can carry to term, I wouldn't worry. Also, it's very possible her body is just preparing for labor. Many women have contractions and dilate during the last month or two of pregnancy, walking around dilated to 3-4 centimeters for a month before they go into actual labor.

I would suggest she drinks plenty of water and lays on her left side, trying to relax when she starts contracting. Five weeks is a little early, but the dates could be off too. I'd call the doctor and see what they have to say. If they express concern for her going into preterm labor then I would avoid sex. But otherwise it's perfectly healthy and okay for women to have sex up until they're in late term labor.