chest pain

I had some moderate chest pain that felt like I pulled a muscle mid to late pregnancy. it occurred only at night when I slept on my back, so I figured it was just pressure from my belly. Well I am 13 days post partum and the same thing happened to me last night. It happens if I sleep on my back and hurts until I turn onto one of my sides. It's just left of the center of my chest. It feels deeper than my breast, more like muscle or cartilage. Anyone else experience this during and after pregnancy? I never had it before I was pregnant.