By this stage of pregnancy every time you get a twinge you may worry that it's the onset of labor. This is a normal concern, but try to remember that, even though you're heavily pregnant, most aches and pains are still likely to be due to constipation, or stretching ligaments, rather than labor.
You may begin to have Braxton Hicks' contractions; these practice contractions occur as the uterus tightens as a warm up for labor. They also help direct more blood to the placenta in the final weeks of pregnancy. Some women are unaware of them, while for others they can be quite uncomfortable. Relaxing the uterine muscles by changing your position, walking around, or taking a warm bath can help.
If you're unsure whether the pains you're having are Braxton Hicks', always consult your doctor.