Newborn sleep please help

My son is 4 weeks old today and he’s done this for a while now but he’ll usually only sleep 1hr at a time during the day BUT come the late afternoon 4pm he’ll start sleeping long stretches usually Between 2-4hrs. Does any one have any ideas as to why that happens and also any tips on how to increase his nap lengths during the day so he’s sleeping longer than an hour PLEASE tell me. I have a toddler aswell so bub sleeping only an hour makes it difficult to get stuff done and spend time with my other child. It wouldn’t really be much of an issue but my newborn is clingy and when he’s awake he refuses to be put down!!! But really just wanting to know why he has short naps during day then long sleeps in afternoon.

Thanks xxxx