15 month not gaining weight

At our 15-month checkup, the doctor told us that our baby boy hadn’t gained any weight since his 12-month visit and recommended that we try to give him more food and milk.
We have another appointment next month to check his weight, and I’m worried that he won’t have gained any weight by then.
I wanted to know if any other parents have experienced something similar and if their baby ended up being completely fine. I’m just an anxious mom and could really use some reassurance because my baby has recently started playing with his food and often won’t finish his meals. 😞