Talk to General Physician on Weight Gain

I'm really very worried about my weight gain...we r identical twin sisters and start se hi hmari height weight sb same hota tha and hm dono bht smart hoty thy...problem ye hai k pichly kuch arsay se mera weight kafi gain ho ra suddenly i don't know the reason...dieting wghera b start krti but 1 to 2 kgs loss hota but next week phir gain ho jata ... mera weight is wqt 70 kgs hai....or height 5.6 hai or age 20 hai....jb k meri sis ka 55kgs hai...mn bht preshan hun mera weight kesy km hoga ....belly fat bht zada ho gya side belly fat b neck hump double chin chest fat....isko kesy loss kru? Kia weight loss ki koi mdcn hoti..plz doctors reply