Girls, hello! After cesarean I didn't tighten my stomach, at first it …

Girls, hello! After cesarean I didn't tighten my stomach, at first it seemed normal, gradually it seemed like it stood in place. But already 3 months have passed, and I noticed that my belly became not like before, it started bulging out, as soon as I eat or drink something, and just like that. Is this because of lack of physical activity? Or is it because I didn't tighten it? What should I do so that it was like before? Before I could wear fitted clothes and it was fine if I slightly tightened my stomach, but now it's terrible?? I have complexes now?