What could be the the possible reason of my weight gain? Went from 101lbs to 147.7lbs in 5 yrs. No thyroid problem. But have a sedentary lifestyle.

Die diet diet. rapid weight gain is most of the time attributed to high grain/carb intake. limit to no more than 50 grams per day while increasing good fat and protein intake to avoid hunger issues and allow long term adherence. go paleo !