When will my period come regular again after having a baby?

Hi my name is Gracie im 16 years old. I Have a 5 month old son and I only got my period once since i had him.Is that normal or is there still after birth in me? I'm like really scared I asked my OB doctor and he said my body might not be getting vitamins like it should after i had my son (Melliki),give me your advise and what you think please :(