I just re-read your post...you say you know this is what you are dealing with. You don't have a definitive diagnosis? If not, I highly suggest you try to get one ....
in Cookie's case, I took her straight to a specialist and did the diagnostics so that I knew for sure what we were dealing with. There are just so many things that could be going on.... here is a good link:
Intestinal Lymphangiectasia - Mar Vista Animal Medical Center
For instance, if it was histoplasmosis, certain meds are needed.