Husband not sure about ..

I have a 5 year old from a previous relationship, my husband and I just got married 3 months ago.  I am so excited and ready for another child and one with him.  He however is not ready and I'm not sure if he ever wants a child.  This is something we discussed before getting married and he was all about having a child before.  Now he complains often and says how much work it is and how expensive.  I'm not sure what to do! It is so important to me.  Has anyone ever experienced this?  I feel like it's causing a huge problem in our marriage already.