Unexplained Weight Loss, Headache, Stomach Pain, Feeling Hot, Menstrual Irregularity

I am 46 years old and have been overweight most of my life. Starting in January of this year, i rejoined Weight Watchers, an lost 45 pounds over the next 6-7 months. It was slow but steady and I reached my goal weight. I workd hard to keep it there. then all of a sudden, during the second week of august, i began losing weight without trying I expected to gain weight when I went out to a buffet for lunch one day, and then continued to eat alot all weekend. when I got on the scale on Monday, i had lost 3 pounds. it seemed like that weekend of overeating flipped a switch. Since then,i have been very hungry, especially first thing in the morning, and it seems I can eat anything I want, and I am still staying at the same weight. I have not been exercising at all. The only other changes I have noticed is headaches a few times a week, i get hot alot, and have occasional pans in the left side of my stomach . But that could be the stress of worrying about this. I have also had some menstrual irregularity this year. I went for almost 2 months with no period, then had it several times with only a week off in between. Everything I read points to cancer and I am terrified that is the problem. i don t have alot of money to go to the doctor for alot oftests.