I'm 5.5 months and my ribs and back already hurt... is that normal?

It is normal. Try sitting straight I know it's tough I too am a sloucher😳😳 .. If it doesn't work just try laying on your left side for a while. Always get some rest when you feel achy. If it doesn't work at all just mention it to your doctor next appointment or give them a call. Good luck hun🌸