If your toddler is not gaining any weight, then find out the reason. As doctor said, it could be feeding issues. You should also check with your pediatrician, he can find out any underlying problem such as any disease or any other issues. Check if sleep is proper or not as improper sleep is one of the reasons for not gaining weight. Give a balanced diet and don't worry. Sometimes toddlers gain very slowly
Please check with a pediatrician. Check out for other growth factors as this could mean some sort of developmental delay. Check the diet, other behavioural symptoms that could be reasons of not gaining weight.