Dirty nappy

I’m a new mum and my baby is three weeks old today. Since yesterday she started to poo more, first it was very runny and yellow and the rest of the night and today it’s been more mushy but still pooing very often, even while changing nappy she goes. But she is sleeping and eating well. Can it be the formula? Is it something else? Since is Christmas eve everything is a bit more complicated, I called my GP but not working, so I called 111 and still waiting for someone to called me back with advice.