Aih, sabar ye mak, gastric macam ni memang boleh drag on even after demam hilang, few days lagi biasanya okay one. The ORS and air garam tu dah betul, so you're doing the right thing.
From what I hear from mums around, sometimes the tummy needs a few more days to settle balik, especially kalau ada muntah involved on day 1, it can take a bit longer for the system to recover. Tapi tu la, some kids pun memang ada temporary issue with certain milk while their gut is healing, so it's worth asking your doctor kalau should try something gentler in the meantime (like diluting with more water atau switch to plain rice porridge + broth dulu). Either way, I think if the cirit birit drags past 5-6 days or kalau ada tanda lain (darah, atau dia laging lethargic), that's when you check the pakar, better safe than sorry with first kid kan!
Fingers crossed dia recover quickly for you, mak. Lepas demam hilang biasanya cepat juga the energy comes back.