Three days doesn't seem long, Blodwen. It might be a good idea to follow Jo's advice, though, and post your menus so that they can be checked for any potential pitfalls.
Hang on in there. I didn't lose anything for the whole of last week, but this is something which can happen occasionally for all kinds of reasons - water retention, TOTM, hormones playing up. Don't lose hope. Plenty of others have got through it, so I'm sure that we can, too.