WWW, please don't beat yourself up. PMT makes anyone feel awful at the best of times. I always feel at least twice my usual size, and in fact, make a point of never going shopping just before my period comes - it's just too depressing.
I second WWB's prescription of a hot bath and a glass of wine.
See how you feel in a week's time, but I think WWB's right that slimfast is not really the answer. (I think you secretly know that too!). Yes, it would be a quick fix, but would it really help you in the long run? Remember, we are all here for the long haul. I've been posting since the beginning, but not trying to lose weight until my emotional baggage is more sorted (I'm seeing a counsellor).
However, I have to admit to feeling extremely when I see the weight losses of those who have really stuck with it, for 7 months now. It is worth considering the long journey, not just the short sprint.
We all understand how you feel, and are here to support you.