Need to lose 20 kgs. No thyroid problem.

I have been gaining weight irrespective of whatever diet or physical activity I do, I was normal weight of 60 kgs 1 year back and I have gained 13 kgs in last one year. I am not able to lose weight no matter what I do. I go to gym every morning , I walk aa much as I can entire day. I avoid sitting down during meetings, I avoid eating junk food. Mostly its roti and sabji for dinner and lunch. I am not able to understand what should I do. I am getting married in 6 months in December and I want to look like my old self for the wedding. I am losing self confidence because of my weight gain. Please help me in understanding what I should do to lose weight. I have checked for thyroid twice till now and there is no thyroid problem.