Oh I am sorry!!
I do agree with OHIO 76 though. It really could be a number of things. If it is a fistula then you must take the prize for "fastest fistula grower." Display that trophy on your fireplace mantle!
I am thinking it is probably just infection that is clearing out of your body. Drainage often doesn't smell very nice -- your body is trying to get rid of something. Or maybe you have a new infection. Not hard to get in the abdomen. And it is usually not because you haven't done a good job of keeping things clean, rather you had an incision and they can get creative about infections all on their own.
So put aside you worry for tonight and get a good night sleep.
Let us know what your doctor says! Praying for your healing, and a worry-free night.