pumping??

How often should you pump daily? I pumped earlier in the day for 15 minutes and made about 5 ounces.. and then I pumped again just earlier and made 4 ounces.. primarily from the right breast, my left one isn't really producing a lot as before because I haven't really been feeding my son off that one because it is pretty cracked and hurts like hell.. so I decided to start pumping and I can't even get an ounce out of the left one.. so I'm wondering how often some of y'all pump during the day? How long you wait in between each pump to start pumping again?