I constantly feel hot?

I had that trouble & the same tests & negative results,it turned out to be my medication once it was eliminated i felt so much better I am now taking another 1 for another problem & its starting again I will give it longer to see if it's just initially as some medications side effects do.In answer to your question that might be your problem if you are taking medication or used or taken something different from the start of winter until now if so try to eliminate that now to see if that solves it.Hope it helps.Good Luck.