I agree with Emily - pain medicine can cause this. However, I must also bring up that thyroid problems can cause hot flashes/sweating as well as. I attributed my problems after fusion surgery to pain meRAB and later found out that the leg cramps I was experiencing and sweating was due to my thyroid. I am sure their are other medical reasons for causing this so if it continues I would definitely bring it up to your doctor. You just never know -- you went thru major, major surgery and it is very hard on your body overall.
Good luck.