Caitlinsmom:
What you are talking about sounds like symphisis pubis separation. The symphisis pubis is the joint between the two pelvic bones, and during pregnancy the amount of relaxin flowing through your body can cause the area to gap a bit, which can be very painful. Movements where one leg raises above the other (such as walking up stairs) will usually increase the pain, as will straddling poses used when getting into/out of bed or the car.
I'm sorry that you are hurting, mama! A support belt to help hold the joint together might be helpful in alleviating some of the pain, and acupuncture or chiropractic work are said to be effective for some women. Hot baths or hot water bottles can also help, and some women find it necessary to limit physical exercise to avoid straining the joint. And to help you get through it, keep in mind that once your pregnancy is over and your hormone levels regulate again, you should experience total relief from the pain.
That said, there is a condition known as symphisis pubis diastasis, where the connective tissues do NOT return to their normal state after birth. If your pain continues after the baby is born, you may want to see your healthcare provider about it.
Hope this helps! Take care, and have a beautiful birth . . .