6 week old not eating as much and sleeping longer?!

So

My baby’s is 6 weeks old and usually on 4-5 oz every 3-4 hours yet the past couple of days she has only had 2-3 oz and eating further apart as she’s sleeping more, she will spit out the bottle or milk and refuse to feed sometimes after an ounce, getting really worried cus all she wants to do is sleep!! (FTM)