Why did I gain weight after starting multivitamins? And What to do now?

I am 45 years old. Just over five years ago I became a vegetarian and have felt great ever since. About a year ago I decided it was time I lost some weight. So I joined Weight Watchers and went from 214 lbs to 183 lbs. And I didn't feel hungry, which was surprising. I felt even better. Despite eating a healthy diet, my doctors advised me to begin taking Multivitamins and Vitamin C. Actually they'd been telling me this for year. All of a sudden I was hungry all the time and subsequently began to eat more and have gained most of the weight back. Can anyone tell my why this happened? And should I stop taking the vitamins? Obviously with my age and menopause in force the Vitamin C is mandatory. But are the others really necessary?