Good grief! Freaky mood swings is one of the biggest parts of being pregnant and each pregnancy seems to get worse! I am 40 years old and 7 months pregnant with #4 and will be crying one moment, mad the next and ecstatic the next. My poor children and husband think I am a nut case!
My favorite part is when other people go, "Oh, well that makes sense since you are pregnant and all." so of course I am upset all over again, like it is not true and I am not emotional. Of course I'm emotional and irrational!
Being pregnant is a wild roller coaster ride and just be prepared, it takes a while to go away once the baby is born too. So just sit back and enjoy the fact that you have an excuse to be a crazy lady for a while.
Good luck and congrats!