Pregnant with second child with a 3 year old toddler.

My first born suddenly doesn't want me to do anything for him. And is very clingy with his father. I have not tell him about this pregnancy as I want to make sure everything is okay till I go for my appointment in 2 weeks time. I'm currently 4 weeks. It makes me so upset and I miss my first born. He only wants his father for every daily activity.