Hi Al
From what you are describing it will be the chemo putting you into early menopause, I went through the same thing and as I am 52 and on tamoxifen am still going through it ! I can't remember after how many chemos it started but I was certainly having them by the end of 6 cycles.
I am now taking a very low dose anti-depressant to help and have only taken it for 2 weeks but it seems to have helped a bit. I have adjusted my life to not drink hot drinks in the morning when I get up cut down on alcohol and always have a fan with me. I drink lots of cold water and have it by the bed too. I also try and wear cotton or "breathable clothes to try and keep as cool as possible.
Good luck
Sarah x