Tinydance's post in Dealing with my gfs mood swings was marked as the answer
How often do the mood swings happen? Some women do get bad PMS once a month before getting their period. I become sad and teary and a bit moody (and very hungry lol) about a week before getting my period. But the low mood only lasts about a couple of weeks or so. It's not really normal to have mood swings all the time. That might be more indicative of a mental health issue.