Restless! It’s 3 AM pls help

We had a long day today out at the shops. Our 20 week old is great outdoors and typically takes short naps in stroller but always super exhausted afterwards.

We are definitely paying for it tonight, it’s 3 am he’s been up on and off since 1 am restless. He falls asleep easily but 10/15 min after being placed down he wakes again. It’s obvious he might be overstimulated from the day we had or super overtired. I could see how tired he is.

Does anyone have tips on how we can help him ? I don’t even care about being tired myself I just feel so bad for him.