I had this a few years back when I was 35, thought I was going into menopause, and my GYN said it was due to being underweight for my body type. I had lost a few pounds, not much, just about 3 or 4 lbs, and apparently that was enough to make a difference. I gained a few pounds back, adn the night sweats went away. A year later, I dropped a few pounds again, and the sweats came back. Gained a few pounds back, the night sweats went away. He said that everyone's body has a set amount of fat it needs to make the estrogen it needs to function properly, and if you go below that, you'll get basal symptoms, like night sweats, and other things. I fought him on this because I'm by no means skinny. I'm 5'2", normally about 110-112 lbs, very hour-glassy, with chunky thighs and knees (in my teen years my little brother used to call me Bettie Boop!), and I dropped to only 107 lbs. when I had symptoms (and my legs were still chunky!).
Anyway, fast forward to today, at age 40, and I broke my foot at dance class a few months ago, just getting up on my toe to turn. Was told that I am early stages osteoporosis, and now have to be super careful not to fall for the rest of my life! I have received numerous lectures about staying in a healthy weight range because estrogen is protective, etc. So, long story short, all you younger women out there, take care of yourself, don't compare youself to others, and stay healthy! Embrace your curves!!!
I hope this doesn't sound too lecture-y, but I've been stuck elevating my foot for two-plus months, and it sucks. I've been lecturing my own daughters on keeping healthy and listening to their bodies so they won't end up with a broken toe that won't heal when they're older like me! If you're in your 20s and having night sweats, please listen to your body!!