What Causes Night Sweats?

I am 25 years old and I currently weight 175 and am 5 7. I have over the past 2 years been increasingly gaining weight. I exercise 3 times a week, have tried every diet, have seen a nutritionist, and a family doctor. Everyone says that I am doing everything right but they can not explain why I keep gaining weight. My other symptoms are I only move my bowels once maybe twice a week, I get random hot flashes, I have night sweats, I am tired and moody a lot. I am not on any medication and there is no way I am pregnant. Thyroid problems run in my family but I have been tested and everything came back within the normal range even thought I have most of the symptoms. I started my weight at 160 this year and just keep gaining weight. If you have any ideas on what this could be please let me know. I have read that not all people with hypothyroidism can be proven with the tests but if this is true I don t know how to be put on medication if I can not have a doctor prescribe it.