Whenever I get coldsores I eat lots of yoghurt and beans. It seems to lessen the severity of it for me.
Maybe ask your chemist about Zovirax too, I know it use to be on presciption only, but is over the counter now, so it might be suitable for you to use? I got a what I thought was a coldsore after DD was born, my mum went to the chemist and he gave her something for me to use while breastfeeding, but I can't remember what it was??

Hope it goes away soon, nasty things they are

Nic