How to get rid of tummy?!?

I'm 5'4 and 120 pounds. I have a small frame with small boobs and thin arms and legs. For some reason though I have always had a stomach that I can't get rid of. My boyfriend once poked fun of it and said it was "disproportionate". I'm starting yoga and pilates this week because I heard it was good for the core. Has anyone else had success with getting rid of a belly like this though? What did you do?
How to get rid of tummy?!?
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