Staci, when I found out that Carina had gained 8lbs over the winter, the vet also did a thyroid test. Since everything was normal, and the weight gain probably the result of too many treats and too little exercise, I cut back on her food and started to add green beans and carrots to her dinner. She loves it and has lost 4lbs.
You could ask your vet is that would be of some help, in addition to the food he recommended.
Please give Keegan a big hug from me.