Is it hurting because your muscles are cramping (that can be a side effect of increased mobility in your pelvic joints or synthesis pubis dysfunction). If that's the case, as well as your stretches, you might find some relief/release by leaning on a tennis ball against a wall over the sore spot (bit like having someone do a massage for you in the spot you can't reach). You might also get some relief by sitting in the bath/standing under the shower with the hot water and then try your stretches...?

Hope that helps, all the best with your upcoming labour.