Aw hun, I'm sure it's a normal thing. My periods can suddenly change pattern, they seem exactly the same length of time for years then suddenly only last 2 days or suddenly go from 4 days to 6. I am fairly sure it's caused by stress. It happened to me when I was stressed and it just seemed to throw my whole body out of wack. And Louise is right, just ring your docs and ask for an urgent phone appointment if you need quick reasurance.
Louise sweetie, your avatar is heartbreaking!! Are you very sad at the moment?