my stomache

[Daisy_]

Kay so I weigh about 104 llbs and I am about 5'5 at the most I think. I'm not fat by all means, but when I sit my stomache is fatty but when I stand it isn;t? Why is this just natural? or what can I do to help myself feel more confident? Sit ups? how many? morning time night time?
Thanks for the help ladies