I brought my rat to the vet about two weeks ago and when they weighed her she was 285 grams. Last night I noticed she seemed thin so I weighed her again and she is now weighing in at 255 grams. I am wondering if this is a normal amount of fluctuation, or if I should start to worry? I have not changed her diet and other than the weight loss she is acting normal. Shes about a year and a half old, eating oxbow adult rat food.