formula

so I've been exclusively breastfeeding my son Leo, who is 14 days old. It was my plan to only bf until we introduced solid foods, etc. However, over the last few days my milk supply has not been totally satisfying him. If he could, he would be on my breast 24/7. I've weighed him before and after feedings and he seems to average 1.5-2 ounces each time. However, moments later, he goes back to the breast acting like he didn't even eat! What should I do?Should I supplement with formula? I have a 17 month old as well, wlso I don't exactly have several hours to spend pumping every day..