When I had to make my 7 year old cocker lose 15 lbs My vet suggested not only cutting back the food but feed her in the am and that way she had all day to use it up and not have it just ad fat at night. It worked great in 6 months I had a great trim girl.
I have been using that for myself latly and in the last 2 months I have lost 18 lbs. I eat just veggies or soup at night and now just got 30 more to go. Hope this helps.
I don't know if the seasons have any thing to do with it but Merlins starting to get the springer butt spread too. But it's been in the 80's here and he's too hot to play. Cutting back his treats and food too.