How long does your baby nurse for?

I find her feeds getting shorter and shorter, and she still sleeps a lot. She’ll sleep longer stretches at night, as well (different experience than with my first). We thought she was about 11 and a half lbs and she was 10 lbs 13 oz at her 8 week check up yesterday. Just worried about her losing/not gaining weight. The doctor didn’t seem concerned as she was still close to her curve from earlier. But that doctor didn’t seem to hear any of my concerns🫥