I have a four year old American Staffordshire terrier and he is on Thyrocab for his thyroid. Had symptoms of weight gain and lethargic so my vet put him on. Now five weeks later, he has lost a lot of weight and his coat has turned copper and now gray on his back end. He was a jet black color and is no longer. In the sunlight you can see there is something wrong with his coat. Not loosing hair but it is turning upward and has gone gray. this has happened rapidly in the last week or so. Should I take him off the meds, or could there be something else causing this?