Redistribution of your body fat/water composition. You will find your weight has come back to 'different' places. Previously, I was a major pear shape. With regain, I am finding the weight settles on my stomache first.
i am just getting in to a size 20 & 15 stone. the last time i was 15 stone was just b4 i fell 4 my youngest (7 & 10/12) & i remember buying size 22 pair of trousers so i'm in the same situation as you !