Night owl

My baby girl is 4 weeks old. She sleeps around the clock but this week she has been staying awake after feeds at night. She usually doesn't cry she just stays awake and kicks the blankets off and makes little noises for around an hour after each feed during the night... Sometimes she cries and I just out her back on the boob.. I'm not complaining I just find it hard to go to sleep when I know she is awake. Is this just something that happens when they get older?