6 months pregnant and haven't felt baby move in 2 days?

I'm 6 months pregnant and haven't felt the baby move in 2 days.. the other nite i had this horrid pain and she got really stiff like a ball .. and i haven't felt the baby move since. i can feel where she is.. and no matter what i do she doesn't move. she usually moves constantly the moment i relax. Especially when i lay down. I've been in bed all day laid on my left side, on my back, everything she hasn't moved i'm worried. i've felt her movements and known where she's been since 18 weeks.