Rib pain

I'm 25 weeks, the last couple of weeks the pain in my ribs has become progressively worse. It's at its worst when I'm trying to rest like lying or sitting on the sofa to watch tv or in bed, I can't lie on my side for longer than 5 minutes without having to move. I'm having to sleep sitting up with my pregnancy pillow pushed behind my back and ribs to take some of the pressure off. :(