Crying all the time

I don't know why but I have been super emotional lately I'm 30w4d and everything my fiancé does or says makes me cry and usually I'm the one who gets mad at him for nothing and I feel bad and all and I know he doesn't understand why I am like I am heck I don't even know why I am... I heard crying and being upset is bad for baby so that's makes me even more upset when I get to a frustrated phase to where I'm bawling my eyes out.... I feel like a bitch right now and I don't know how to address it to him that I'm sincerely sorry for how I act sometimes.....