Post Baby Body

I have a wonderful six year old son who is the joy of my life. I had to deliver him by cesarean because of complications. And as much as I love my son, I really hate my post baby body. Before getting pregnant, I was very small, only weighing 97 lbs. At the end of my third trimester, I was 140 lbs. And most of that weight went to my stomach. I have tried dieting and exercising for a very long time, but I haven't seen or felt any changes. I am very insecure about my stomach. I haven't worn a two piece swimsuit because I'm afraid of what other people may think about it. My SO on the other hand isn't bothered by my sagging skin and stretch marks. To try making me feel better, he'll lift up his shirt and show me all the stretch marks on his stomach and joking say "Look at my fat ass. I have more stretch marks than you". Even after we make love, he likes to kiss my stomach and lay his head on it. But still, I just wish I could fix the way my stomach looks. I look at how other women bounce back to their pre pregnancy body. Then I look at myself and wonder what I am doing wrong. Especially after 6 years. I've even contemplated getting a tummy tuck in hopes of solving my problem. I just feel very insecure and defeated right now.