First week breast feeding help.

I had my baby last week and am primarily pumping milk right now and occasionally feeding right from the breast - he's slightly premature and a few seconds after he suckles he falls asleep. The pump I'm using seems to be irritating my nipples as they're very tender and a little swollen/red. I'm using lansinoh cooling relief pad things and also the paste as much as I can. Is there anything else I should be doing? How long can I go without expressing milk without it effecting anything majorly? I only express enough for one feeding about 1oz - 1 & 1/2 oz and can temporarily supplement with formula for a feeding if it would help