I couldn't lose any weight while nursing! If I cut back calories at all, my supply would tank. But it sounds like your LO is starting to get nutrition from other sources, and taking in less calories from you. For a long while, I was calorie counting and around this point I started adding in only 300 calories instead of 500 per day. It sounds like it's time to rein in the eating
I nursed both my older kids until they were about 2 years old.
I've never been able to really slim down until I was done nursing.
Not sure if it's a psychological (I'm nursing, I can eat!) thing or physiological.
But experience does tell me that as I start to move toward weaning (i.e. nursing less frequently), I also need to reduce my calorie intake to compensate or otherwise I gain weight.