Could this behaviour be PMT?

[Cuddleczar]

Just had the most awful week with my youngest DD, aged 15, who basically fell apart, couldn't get herself to school (ended up with several late detentions), had massive fights with friends, was really aggressive to me and DH (swore at us, which is most unlike her), swinging from being OK to total anger with everything in the space of a few minutes. Then her period arrived. And she is now feeling really good and calm. She says she was worried about herself that she was going to have a complete breakdown (I was also worried about this). Does this sound like really severe PMT? Her older sister also suffers this. Both of them are already on the pill (the older DD for control of PMT, it has helped significantly) and the younger DD for control of acne and heavy periods. Should I take my younger DD to the drs to see what else they can suggest? (Though my older DD says she asked this last time she went and there wasn't anything.) Seriously, if this is PMT, then I fear for her relationships/career/school life!!