Hi Ladies, thank you for replies.
When I went to loo late last night I wiped and there was a smear of blood. I have only had about 4 periods in the last 12 months, so this was unexpected. I have looked online and there is info on something called "period flu" and US term I think. This includes muscle/joint aches, chills, fever and shivers amongst other things. The chill/shivery feeling last night did not develop into the full rigors and eased as soon as I went to bed. I am still a little achy this morning, but I slept like a log until very "urgent" diahorrea woke me, which I often get around start of a period, so I think this is all pointing to a severe PMT reaction, rather than anything more serious. I will take on board all your advice and monitor, and get second opinion if its not starting to ease, but definitely better than yesterday.
Thanks for all you help xx