losing weight

have an underactive thyroid and really struggled for about 4 years with my weight! it just keeps creeping up no matter what exercise or diets  i try.I went to my doctor last week in desperation and am now on xenical.Will it help ? i dont expect miracles,doctor said i wasnt eating enough ,but i know if i eat more weight will pile on....Would be great to hear off anyone with similar proplems or anyone with suggestions ...Thanks