I am working for Robb Stark as a mercenary and I can never seem to join a castle siege for him or in general do anything past kill murderer, collect taxes, kidnap someone or gets cows.

What is this issue?

I also noticed when I first worked for him he paid me $1600 to do nothing for months and months but now he only pays me $900 to help during the war, what gives?

I just want to join some proper fights...