How often do you pump and how much do you get?

vespa42

I have been pumping at work and as DS gets bigger I am growing a little nervous about my supply and if DS is eating enough.  I work 13 hour shifts, I pump 6 times and get on average 18 ounces.  It usually varies between 3-4oz when I pump although occasionally I will get 5 or 2.  DS usually eats 3 or 4 5-6oz bottles and I feed him before I leave and when I get home if he is still awake.  Does this seem normal/right?