Losing weight/ getting in shape

So in the past 5-6 years I have gained a lot of weight ( a lot in my eyes) I was about 180 for a long time but now I’m up to about 240 and I would really like to lose 40-50 pounds. I’m planning on going back on the diet my dr put me on when I was pregnant, anybody else have any suggestions as to what else I could do? Posted pic for visual first pic was junior prom on 09 with my now husband and second pic is me on my wedding day august of this year.