I’ve just started a diet 3 weeks ago. Weighed myself last week and was 11 stone 4, weighed again and was 11 stone 8. I’m really annoyed because I’ve been really good with my eating, and been out running 4 times this week. I’m on my period this week - will that have an effect?
Yes, it causes water retention for a lot of women. If you have been running a more than usual, that may be compounding matters, as the muscles retain water as part of the damage repair process. There may also be an increase in your cortisol levels due to the physical stress of increased exercise, which again can lead to water retention.
Make sure you're drinking enough, and see what things look like next week.