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Less bleeding during menses can be due to hormonal
imbalance and it should not cause increase in tummy size.If you are having less bleeding consult a Gynaecologist for examination and she will examine you and advise accordingly.To rule out any problem inside your tummy you can get done a sonography
of abdomen to see if you have any cyst
or any other problem.If every thing turns out to be normal then start doing abdominal exercises
and the tummy size will reduce and the abdominal muscles will get toned up.