I've got the same problem and my midwife said its the ligament stretching pain but its painful :(
Its spreading and ligaments loosening! I just talked to my Dr about it. It hit me so fast I could barely walk and hasn't stopped Lol it feels like your croch is breaking my Dr said that is pretty much what's happening your bones are coming apart making room for baby!
I'm 38 weeks too and feel the same thing! Its because the bones down there seperate for birth and its just your body getting ready.
I have had the pain since I was at 16 weeks it's terrible and makes it so hard to move when you're sleeping try to sleep with a pillow between your legs
Ugh I have had this too lately and I'm only 31 weeks. Its soooo painful and I told my doctor and she said its normal
Maybe it's labor or your cervix is slowly dilating