That's not too slow at all! Pretty common for weight loss to slow down the further along you are. Think of it this way: to lose 1% of your bodyweight at 300 lbs you lose 3 lbs, to lose 1% of your bodyweight at 200 lbs you lose 2 lbs.

Plus you have to keep decreasing your calorie intake as you get smaller and your body needs less to maintain its weight.