Has your doctor talked to you about being induced? Or are they waiting it out? Csecs are always the last resort, but you still have time to be induced. I would do lots of walking and have good old fashioned sex to naturally try to speed up the natural induction process. Hang in there, you're almost home!!
Prostaglandins is a hormone that can induce labour. A man's semen contains this hormone. Oxytocin also causes contractions and a woman's body produces it when she climaxes. If there are no health reasons for you guys to be abstaining right now then some quality time together might get things moving along. It only does the trick if you are getting close to starting labour naturally though because the amounts are small. If it does bring on mild contractions then a walk can encourage them along. I hope everything goes well for you!
As this being your 3rd child, I'm sure you're aware of the old wives' tales - sex, eating spicy food, walking & I'm sure there are more but the thing is there's no proven method that will induce labor. When was your u/s performed? The later in pregnancy, the more inaccurate for dates they tend to be. If your u/s was performed in the 1st trimester, chances are that your midwife's calculations are accurate.