Most tkr patients have some swelling and warmth to the knee that can last up to a year. Additionally, as this FAQ says, blisters are sometimes reported at the period of maximum swelling, as there is no more room for swelling or fluid to go within the skin so it forms blisters. If you are not experiencing swelling, or if the swelling or blisters are painful, a call to your doctor may be in order to make sure you have not developed an infection or other problem. Has your physical therapist seen these blisters? If so, has he/she said anything?
Here is some information on hot flashes and what you might do to manage them . It might be a good idea to speak with your doctor about your symptoms to try and determine their cause. He/she may have some insight on whether these flashes could be related to your hip replacement or menopause.
While I cannot provide medical advice or diagnosis on this board and do not have experience with knee replacement, I did find this piece from the New England Muscoloskeletal Institute that discusses blisters near the incision site. It says that the best thing to do is to just ignore the blisters and allow them to heal on their own.
I am so sorry that you are in so much pain! I hope that the doctors are able to find out exactly what is going on, and that you are able to get some relief from the pain. I also hope that you are able to receive any help or support that you may need from this community. Please keep us updated on how you are doing!