Nipple shield 2 week old

My son will be 2 weeks old on Saturday. He starts choking and gasping for air often when feeding. It scares me. Is this ok/normal? Is there anything I can do to prevent this? I think he's getting too much milk. Hes always covered in it. I use the lansinoh 24mm nipple shield. Is there a smaller one? I've been using the shield since coming home from the hospital because my nipples were so sore and chapped. I didn't want to give up so easily like I did with my first. I feel comfortable using it and sort of don't think I can breastfeed without it. Any advice?