There is a prescription antiobesity medication of for dogs called Slentrol. It seems to curb appetite and dogs do lose weight on this medication. They lose weight slowly and safely on it.
If your dog still has trouble losing weight than a thyroid blood profile, and tests for Hyperadrenocorticism should be performed.
Thanks for your feedback. We have already had the bloodwork done for the thyroid and all came back normal. I will look into the other recommendation and talk to our vet. Thanks again!