Baby sucking less

My baby will be 2 weeks old tomorrow and has lost over 1 lb since birth. I've been working with my pediatrician and a lactation consultant. Yesterday the lactation consultant said I do need to supplement with formula and that baby's latch is good and her suck feels good. Last night was the first night I gave her a bottle for her overnight feedings from what I had pumped in addition to offering the breast after she finished a bottle. Today I've noticed that it doesn't feel like she's sucking as hard as normal. Is she getting nipple confusion? Or are my nipples just less sensitive now that she is 2 weeks and starting to heal? I'm so worried about her eating that it's driving me nuts and consuming my life. It's so hard!