Hi Cat, welcome.
I agree w Carol and Sue, you just need to be patient.
This is my fourth or fifth serious go at low carb (many false starts not counted). My loss pattern has been different each time too, although does seem slower and tougher as I age...
I've been predominantly low carb since 2009, and from what I've seen in those 4 or so years most people will lose about the same amount of weight (in proportion to their starting weight) over the first month. Some might drop a ton in the first week, then plateau for 3 weeks, some might lose relatively little the first week but keep on continuously losing a little week after week - and all variations in between.
I track my weight daily (on the 5 pound challenge mainly, link here :
http://www.3fatchicks.com/forum/atki...ml#post4954683) but I don't freak out about the occasional upswing. And prolonged stalls just help me look for new things to try to improve my diet.
I'm about the same age as you and I have found that I need to watch both carbs and calories in order to lose - and I've seen that turn out to be true for a great many women over 40. Men and younger women are luckier - and yes, men often lose much, much faster.
If after a few weeks you're not losing at a pace to keep yourself motivated, please share a few days of your food - often the collective experience here can help identify what some of the problems might be - but for now, it looks like you're doing great!
Good luck! With patience and persistence you'll get there.