I recently posted about my cat that has been losing weight, but is acting normal. He's eating, drinking and even meowing to go outside. He's been tested for FIV, FeIV and hypothyroidism and it's all clear. However, the vet said he had a high fever and gave him antibiotics and anti-inflammatory medication just in case he has an infection. There are zero signs that there is something wrong with him apart from this weight loss. His side's appear more caved in and I'm lost at what else to look for. Even worse, I noticed that my second cat also is showing the exact same weight loss in the sides (you can also feel their spines more, so they definitely have lost some weight). They're not light or severely underweight where it would cause problems, but it's concerning. I just have no idea what this could be since BOTH have it. Any help would be greatly appreciated. They are both outdoor cats.