Is there a hormonal or physiological change after a tummy tuck or body lift that causes intense increased sexual desire?

This is consistent with a collection of blood under the skin flap.  I don't know why the drain was in place so long, but your story is in line with what is expected once a collection of blood turns liquid and starts to drain out.  This usually resolves without too much trouble, but...

Its really hard to tell from the photo, but you could have lost fat there, or there could be an issue with the body wall....that's a good one for a physical exam.  You might be able to excise some skin, or perhaps graft some fat.

HiAt 2 weeks post Tummy tuck most pts are walking upright with little discomfort. It is not your fault that stitches have popped at this stage. It may be that dissolving stitches were used and there was not enough deep stitching done to take the strain. Best thing is to explain you are not happy...