Religious people say that we are selfish for just being what we want to be... Isn't the fulfillment of pleasing your god a selfish act in itself?

This would be like my parents always telling me that I HAVE to be a doctor. What if I'm just not the person to be a doctor? Am I selfish by wanting to be something other than what I'm told to be? Isn't the fulfillment of helping others and being "selfless" actually selfish in itself? If no one was selfish, would happiness exist? It certainly couldn't!