Panting when the weather is not warm is a sign of your dog in pain. You dog might have the bloat which is life threatening. I know this is not the kind of thing a dog owner wanst to hear on a wintery day... This happened to my black lab some years ago, the stomach fills with air and the dog can't release it. I have heard it described as the stomach turns or twists and cuts off much needed blood supply, which left untreated results in death. If this is what's going on, your dog needs immediate medical attention and surgery to correct this. I am not a vet. I just know this from reading dog articles and it happened to my dog. Mostly it occurs to larger breed dogs, but it can happen in any breed.
I had almost the same problem a few weeks ago with our 14 yr.old. The difference was that he was not panting.He had a good appetite,he eas drinking well there was no other symptoms except that just like your dog he could not be still for any longer than 30seconds. He was constantly moving locatons or positions.He is now fine.
Your problem sounds more serious. I don't know what to tell about the weather conditions.
I hope Jaybay can give you more and better advice because my dog is doing fine.I have not had any more problems.
I hope the same for you
PawPen