Cramping when lying down

I am 6 weeks pregnant with my 3rd child and sleeping is already impossible. Not because insomnia, frequent urination, or anything like that... But because when I lay down on either of my sides, even with a pillow between my legs and under my tummy, I get cramping and mild pain. It feels like a lot of pressure on my tummy. These pains are similar to menstrual cramps. Is this normal? I remember feeling this way in my third trimester of my last pregnancy, but why I am feeling like this so early only in this pregnancy? I know my dates are correct, and that I am in fact 6 weeks along. I try to go to sleep on my back with my head propped up on pillows, but I always wake up on my side in pain. Any suggestions?