How To Improve Weight Of Baby While On Medication For Iron Deficiency?

I have a 18 month old recently lost weight shes tired and all she wants is cuddles she having test but 1 came back that s shes iron deficiantl so on meds for that .I worried sick ive put her on a gluton free food on recommendation of the doctors at hospital how can I help her to eat more shes drinking plenty of milk too when can I see or expect an icrease in her weight