17 days post op Tummy Tuck, why is my stomach swollen and hard?

It is common to experience swelling after a Tummy Tuck. You have to wait until it goes down 3-6 months so you will see your final results. 

Swelling after an abdominoplasty is normal and if this was combined with liposuction
(especially if the stomach area itself underwent liposuction). Without being
able to examine you it is impossible to say if this is a normal amount of
post-operative swelling. If the swelling is increasing and the skin getting
tight this could be a seroma (fluid collection) or a hematoma (collection of
old blood). The best course of action is to call your surgeon and be seen as
soon as possible to evaluate the problem and decide if any treatment is needed.

Thank you for the question!  It is difficult to tell if your recovery is normal without an in-person consultation.  What you describe could be normal or it could be the start of a seroma.  Please see your plastic surgeon as soon as possible for evaluation.  Best of luck.--Dr. Mussman