I'm not sure if he's in pain but yesterday when he was lying on the bed with my wife and son, my son touched him and he squealed.
My dog is a lab terrier mix, 17 months old, and no, he didn't get any other medication. He has been on heartworm meds for months.
As far as being cold, my house is kept around seventy degrees. I did put a blanket on him.
As of this time, he seems more like himself.
Thanks to all! I'll keep a close eye on him.