Hi,

I have had similar pains (also felt them in my bum!!!) when I saw my ob he said it was the baby's head engaging in the pelvis, the pains are caused by it pushing down on various nerves.

When it first happened to me I thought they were (very painful) contractions, but they were never regular and the intensity varied too much.

They come and go, but I find the best thing to ease the pain is a nice warm bath and plenty of rest.

Hope this helps,
Clairexx