Do you think it is normal to be SO disappointed with the gender of my child?

i am a nearly 18 weeks pregnant and on friday we found out we are having a boy, i have a girl aged 5 and a son aged 3, i lost a little girl in october to SIDS so this is baby is very wanted but deep down i wanted a little girl and after been told that it is a boy, i have been really upset and disappointed, i love the baby but i just feel like i wanted a girl, its hard to explain, can anybody relate