Hi Tara,
Welcome to the board.
I can't give you exact explanations as to why hormonal BC can play havoc with some women, and not with others, it simply would take too long and get too involved. All I can say is that it is not uncommon for women to start on a hormonal BC only to then find they have worsening PMS symptoms, even if they never had PMS before starting BC. There are several reasons for this. If you want to remind me at another time (when I have more time at my disposal, I will explain the 'why' in more detail.)
And despite Yasmin's claim (and others) there is no BC that actually cures anyone of PMS or PMDD. All that the BC can do for women with PMS/PMDD is regulate the cycle and make it more 'predictable' and lessen the severity of some symptoms for a fortunate few. It is also helpful for skipping menstruation as a means of avoiding PMS/PMDD but I don't recommend doing this for more than 3 months at a time. It is important to allow menstruation to occur as it is the feminine time of cleansing and detoxification of the body. Also, I always recommend going on the lowest dosage BC (which is far healthier) if at all possible. If used correctly, the low dose BC's are equally as effective at preventing pregnancy than the conventional higher dose pills.
Additionally, you might be interested in these links for further info.:
My absolute favorite info. link on all things BC:
http://www.wdxcyber.com/mbcontra.htm
And something else all women should take very seriously (but sadly don't):
http://www.wholeapproach.com/symptoms.html
All the best,
Anthea