You seem to be using the word "calling from God" as synonymous with "vocation."  

All vocations are callings from God, but not all callings from God are vocations.

A vocation is a specific and unique type of calling from God such that your life will change and you can't go back to like it was before.  It is something you can't give up.  Again, it is who you are.  Some callings from God can involve a career path or job.  A vocation is who you are. You can never give it up.