I have had this for some weeks now. It could be Symphysis Pubis Diastasis, which is what I have. Its where (and Alan correct me if I am wrong) the joints are all soft due to the Relaxin hormone, but sometimes they soften too much and this is where the pain is caused.

My midwife told me it will stay with me now. I have it really bad today cause I was on my feet all day yesterday. You should sit down when getting dressed, and when you get into the car go bum in first then swing your legs in. Also keep your legs together when chaning sides when sleeping. It is bad when you stand on one leg, putting too much pressure on just the one leg.

Mine is good some days, then bad others. I have got used to it now.

Good luck!