I also had this, but before the operations. I was moving into an apartment, and spent the day moving things into a truck in early February. I was sweaty and the cab in the truck was cold, then the truck broke down as I was returning it. I had to wait in the truck for close to an hour until the rental company got to me, and my core temp dropped considerably.
I recuperated at a steak place (
) which was nearby and spent most of the two hours I was there shaking. I felt better towards the end, both the food, heat and coffee helping. The real help came when I slept and woke up warm.
It was a grueling experience, and a real showcase of the limitations of the body. I think we tend to forget that we are still healing up until a year. The successes are excellent, but when the body is challenged (as yours was), I would think the areas that are still healing will complain.
I've heard a lot of good advice from people who ski, cross country ski and other winter sports, that the best thing to do is to keep your core (thorax, chest... ) well insulated, since that will help prevent Hypothermia. I defer to more experienced hands at this, but I do think that's what you had.