Both of my dogs are doing the same thing. My GSD Tess, who use to wolf down her food both morning and evening, stopped eating her morning meals, once the weather started to get hot, she'll be 2 next month. Then my 1.5 year old Cairn Terrier followed suit and is even worse about eating, especially in the mornings.
I have to doctor up their kibble (Taste of the Wild) in order to get them to eat, the use to love it, now they just smell it and walk away. They both just lay around all day, won't go out in the yard. I have a couple of friends whose dogs have been doing the same thing. I think it's the heat and humidity.
Although, if I get Tess' leash out, she perks up somewhat and becomes excited. Tess also has allergies, which is another reason she's been aloof lately, she's miserable at times.
Please give your vet a call to be on the safe side. Good luck!