Aih, I know how scary this feels! A few of my mum friends went through IUGR too, one of them had baby measuring about 2-3 weeks behind at 6 bulan, and the specialist told her it could be placenta issues or nutrition yang tak optimal. Since you're having trouble with appetite and mostly berak, this is actually something the hospital team needs to sort out properly, they might check your blood pressure, nutrition levels, and how the placenta is doing during the double scan.
For appetite, honestly most of the mums I know were advised by their doctors to eat small frequent meals (even just a few bites), focus on protein and calories rather than volume, and some took iron supplements or prenatal vitamins yang extra strong, tapi this really depends on what your specialist recommends lah. The good news is, with regular monitoring at the hospital, most of them had babies who caught up or at least stayed stable until delivery.
Definitely bring up the appetite and digestion issue at your hosp appointment, tell the pakar exactly what's happening, sebab they might suggest dietary tweaks or supplements that fit your situation. Wishing you and baby all the best!