Labor

How do you know if your going into labor?? This is my third pregnancy and third baby. With my son I was in labor for 24 hours and didn't really know it because it was back labor and felt like menstrual cramps. With my daughter labor didn't start till I was already at the hospital. I was also a stay at home mom with my other two. This time around in working straight through my pregnancy and I'm scared to death that I will either go into labor or my water will break at work. Or I won't know that I'm going into labor. Is there any signs of labor before you actually go into labor that I can look for towards the end. I'll be 29 weeks tomorrow.