You need to have clocked up 10 posts one any of the Menopause Discussion threads, in order to send PMs.
Most people check for un read posts, when they log on, so if they are following a thread, or your replies, they will catch them there.
Hope that's clear
Oh, also if you want to know when some has replied to a thread click the 'notify' button. Bottom, left next to the reply button.