Can't breathe..

So I'm 24 weeks pregnant with my 3rd baby and I've been having this problem with not being able to take a full breath.. like my lungs won't expand all the way.. has been happening for 4 days but today I've been lightheaded and it's just from the lack of oxygen.. I don't think it's my baby pushing on my diaphragm since I'm not very far along.. should I call my Dr and see what she says or should I assume it just goes with pregnancy..