My child is 9 months old and the nurse said she is not gaining weight properly, do i need to be worried, do i need to see a pediatrician?

Hard to say: The primary reason for failure to gain weight is failure to take in the needed calories. This can also be a sign they are not absorbed, are lost or there is excessive need, or other issues of chronic illness. Pediatricians see these routinely and are a good place to start. The solution to the issue will depend on the findings of an assessment.