Did my stitches loosen up?

It is normal for the tissue to loosen up over time as the swelling reduces and the tissues relax/accommodate a bit. Bulges and asymmetries at this early stage are common as well. You will have a much better idea in 2-3 months. It is highly improbable (though not impossible) that your stitch loosened,

It is a little difficult to give you an answer without an accompanying photo.  I can offer a few general thoughts that might relate to your post.  First, three weeks postop is still extremely early in the recovery process to make any assessment of your results.  Over the 3-6 months following your surgery, your swelling (which may be asymmetric) will dissipate and your skin will heal down its new contour.  Evaluation of the contour before that is premature.  Second, it is normal for the "tightness" you describe to begin to fade after a few weeks as your skin and soft tissue soften and accommodate to the new position.  After all, you want to be able to walk straight without feeling tight!  Third, it is tough to tell you anything about the upper abdominal bulge without a photo (including preoperative comparison).  I can tell you that often time patients who are wearing compression garments around the belly may show some degree of swelling above and below the binder.  This is normal and will resolve.  As always, make sure to convey your concerns to your surgeon who knows you and your recovery best.  Hope this helps and good luck!