Infants decreased appetite

My 5 week old has been a great water (she's probably around 12 lbs at this point). Earlier this week she was eating 4-5 oz every 3-4 hours. The last two days, however, she rarely is drinking 2-3 oz every 3-4 hours. She's sleeping great, pooping normally, and seems to be smiling more than ever. No fever or odd symptoms other than eating less. I will call her dr about this but just wondering if anyone else has had a similar experience. TIA!