Why am I losing weight so slow (1-2 lbs a week) when I used to lose up to 5 lbs a week?

I cut down on my eating a lot. I eat about twice a day now with maybe a snack in between the two meals. I was 261 lbs, right now at 256 so I have lost some but its been very slow. I'm 6ft tall and 21. I exercise a few times a week as well with cardio exercises. Why is it so slow? This past week I only lost 1 pound. I am happy with my weight loss because I heard slow weight loss means its permanent, but I do wonder why its not faster like it used to be.