No fun, I gained all back

This photo was taken 3 years ago and I weigh 110 lbs. I lost 18 lbs and 3 sizes of clothes on this picture. For how much I have lost back then I never ever put myself on diet. I was just doing my regular exercise routine 3 times a week. I was determined then. Now, I gained all back plus 10 lbs and so far 2 more sizes. My mind always thinking of going back to my old routine but my body don’t want to do it, in short or in my own words I’m lazy to do it. I’m thinking or even considering on diet pills. Do any of you friends have taken it? Please share your opinion if you won’t mind.