10 days after tummy tuck, I have foul smell, pus and drainage from umbilicus. What is causing this?

The belly button area is ver particular because naturally ( no surgery related) is a moist area, so after a Tumny Tuck where we manipulate the bb, place sutures and then all of the swelling plus its natural moist, creates the perfect environment for infections. You have to clean it deeply with Qtips twice a day, keep it clean and dry with a dry gauze inside, shower daily and use a wound cleanser right after (no iodine needed). Do not panic. It will be nice and clean following instructions. Dr. Cardenas 

Based on the information given I would recommend you call your surgeon for an evaluation.  Make sure that you are keeping the area clean in the meantime.

Hopefully, it is just a localized problem and treating it the way you are - with antibiotics - may be part of what is indicated.  But you may, also, need wound care.Either way, you need to contact your plastic surgeon.  This is not something you should be treating on your own.Good luck,Dr. E