4 weeks post TT and breast augmentation, no appetite, frequent loose stools going on a week now.

While it does take quite a while to get back to normal after an extensive surgery like you have had, some of you symptoms are worrisome. Weight loss and the severe GI irritability may mean something else is going on like bacteria overgrowth in your GI tract.  I would certainly speak with your PS. 

It is common to have changes in appetite and nausea at the beginning of recovery, but it usually has resolved by this point.  I would normally direct it toward the effects of the medication, but you mentioned you aren't taking any.  I would advise discussing this situation with your surgeon and/or your primary care physician.

Very sorry to hear about your feeling unwell. Did you take antibiotics at the time of surgery, or for a short time after surgery? Sometimes antibiotics can kill off the protective bacteria in your intestine, leading to nausea and diarrhea. 
There is a bacteria called clostridium difficile (sometimes shortened to c. diff) that can take over and cause persistent diarrhea. This would need to be treated with a specific antibiotic that targets this particular bacteria. You should tell your plastic surgeon, and he or she may recommend you go get evaluated by your primary care doctor or even a gastrointestinal specialist. In the meantime, stay hydrated and eat simple/bland things that won't further upset your stomach.
Hope you start feeling better soon!