Shortness of breath?

I'm currently 6 months pregnant. I was doing okay throughout my pregnancy until recently when I started having spike pain down my right thigh to the knee. I realized that my baby was sitting near my back and was on one of my nerves... now recently I'm having shortness of breath by bending down and carrying a 5 lb bag off the ground. Sometimes I feel faint and recently the cramps are more noticeable. Is this normal? Can stress cause this? I'm currently going through a breakdown from my relationship and it has been hard... I don't know what to do anymore