If you are concerned, call and talk to your doctor. Later on pregnancy, women can experience a variety of aches and pains related to your growing baby and the demands the weight makes on your muscles and bones. Our body mechanics also change with pregnancy as does our center of gravity, so women can also unintentionally twist or turn the wrong way causing muscle spasms or joint pains, even in the ribs. It's best to be evaluated by your doctor and he or she can make recommendations to help you be as comfortable as possible.
Good luck!
It all depends on how far you are. How far are you?