Ugh I hate PMT. I get really really depressed with mine, and really snappy. Sometimes people just piss me off and I end up having a go at them for no reaosn, they can just be sitting there and they will still annoy me! Also I eat loads as comfort food and that normally makes me feel worse, so its a downwards spiral really.
I had some homeopathy last year for my skin and various other things, but while I was having the treatment, noticed that my PMT was much better and I was much calmer in general. I actually went to see a practising homeopathic doctor but Im sure you could get something in Boots from their herbal range, you might want to try that.