What is the reason why a newborn is crying and refusing the nipple but will eat with a spoon?

Patient's question:

Patient Age: Newborn, 13 days
Detailed Medical Condition and Purpose of Consultation: The newborn was normal for the first few days. The mother's nipples were cracked, and the baby was fed with a bottle of formula for a day the day before yesterday. Since yesterday morning, the baby has been crying and refusing the nipple. Initially, it was thought to be due to nipple confusion. From 6 PM to 10 PM yesterday, the baby had three bowel movements. In the evening, the hospital was visited for examination, and neonatal gastroenteritis was suspected. Medications (Lianqunning and Ampicillin) were prescribed. This morning, another examination was conducted, and the tongue was slightly red, suggesting possible inflammation. The doctor recommended applying Compound Xinomen and Compound Vitamin B1 powder to the tongue. However, the instructions for Xinomen state that it is prohibited for children under two months old.

Doctor's answer:

You often put your nipple in your child's mouth, or you frequently touch your child's lips with your nipple when your child is awake. It will be fine after a few days.
Do not feed your child with rice porridge. Your baby is still a newborn and does not have a strong digestive system.