dull back ache and some cramping

does anyone else get a dull back ache and a bit of menstrual-like cramping when you lie down? For me, it doesn't matter which side I'm on, I still get a dull ache across my lower back and I generally feel like I am going to start my period when this happens. I dont much notice it during the day. With my last pregnancy, I didnt feel like this, but i did have hip pain from sleeping on my side. i got pregnant again within a few months of delivering my son, so I'm a bit nervous about the short interval not allowing my body to fully recover and causing premature labor.