5 week old decreased appetite

AN • will be having 2 babies about a year apart
My five week old has been eating up to 5 oz every 3-4 hours until yesterday. Now she's taking 2-3 oz. she's 11+ lbs and is happier than ever. She's sleeping well and has no other symptoms. I'll call her dr about this but just wanted to see if anyone else has had this before. TIA!