Mama, I'm glad you already brought baby to the doctor, that's the right call! Since the poop test showed bacteria at may diarrhea pa siya for 3 days, please follow up with your doctor soon if it doesn't improve or if baby shows signs of dehydration (dry lips, less wet diapers, sleepiness).
A few of us mums have been through this, and what helped was sticking to bland, easy-to-digest foods like lugaw or banana, walang oily or spicy stuff, like your doctor said. Keep baby hydrated, ha, and trust your doctor's guidance on whether antibiotics are needed or not. Some cases heal with diet changes alone, pero kailangan i-monitor talaga. Hang in there, mama!