Looks like you may have Pubic Symphastitis....
Hi Ladies
I am 28 and a bit weeks and have similar pain - been diagnosed with pubic symphasitis. Ice packs between the legs, phsyio and accupuncture have been helping.
Started about three weeks ago, and a bit better today than I was last week, but at one stage I could not move my legs without searing pain after sitting or lying for a while which was rather scary.
You need to avoid stairs and any movement which separates your pelvis (so things like breastsroke swiming are a no no).
I would recommend seeing a physio to get some advice on excercises and perhaps a brace (basically a big stretchy elastic belt worn very low over the hips with a padded clasp at the very front over your pubic area).
My husband has also ben given shown how to do some deep massage points on my lower back and buttocks area after applying a heat pad - I have Xs on my back in permanent marker!
Rest is also recommended (but easier said than done!)
Good luck