My Dog Is 3 Years Old. She's So Good, Obedient,

My dog is 3 years old. She's so good, obedient, sweet.... lately, she's been restless at night. Tonight, she's restless, whining, licking her anus more than usual, &, about an hour ago, she was panting hard. We sat with her & calmed her down & she quit panting. But, she's still restless. Her tail is wagging, but she's kind of clingy toward me (female, pack leader). She keeps going to her bowl to eat, but she'a already eaten. From Dec 7 to Jan 7ish, she's gained 5 lbs, even though we never give her table food. feed her 1 cup Blue Buffalo a day, & any snacks are healthy brands.I take her to the park every morning & play with her every afternoon Right now, she's settled down & gnawing on a bone. I'm concerned bc this is very unusual behavior. She's a rescue, we've had her for a year, & she doesn't have any bad habits, like digging or eating anything in sight... nothing that indicates anxiety. She's usually very calm & very obedient.