Not eating enough???

My 4 month old is exclusively breastfed and since day 1 has only nursed from one breast at a time. So she’ll eat from the left side and then two hours late the right and so on back and forth. When she was a newborn she would nurse for about 10 minutes, and as she got older maybe around 2 months it increased to 20 minutes and then 3 months back down to 10 minutes. Now she is averaging like 4 or 5 minutes and then she is done.

We just had her check up and the doctor said she had absolutely no concerns about weight and growth and she was doing great. I just feel like 4 minutes every 2 hours during the day cannot be enough milk!!! (She sleeps from 7pm-8:30am with one nursing session in the night occasionally.) Does anyone else’s baby eat for such a short amount of time??