FTM confused!!!!

My son was born 7/14 so he is only 4 days old. He latched well right away but took some time to get sucking down properly. Most feedings now he is doing well but for the ones he doesn’t I’m pumping and having my husband bottle feed him breast milk. I’m not sure if my milk is really in yet. I pump about 2 oz per breast when I pump. and baby eats but obviously idk how much he is getting. Nothing spills out or anything. I’m also having to use a nipple shield. He was born tiny - only 5 lbs 11 oz and was down to 5 lbs 2 oz at the pediatrician yesterday so I want to do everything possible to get him on the right path to gaining his weight back and avoid formula. Please help - am I doing everything I can?!