
I had this happen a couple of years ago when I, too, quit
smoking and
by the time I could get my doctor to believe that there was something wrong (besides the pernicious anemia, he had already dx'd), I'd gained 30 pounds, was dead tired all the time, my hair was falling out, etc. It turned out that I had hypothyroidism/Hashimoto's thyroiditis. Another issue that can cause inability to lose weight, is insulin resistance, which is the same as pre-diabetes.