Are newborn pamper diapers known to leak? Why is this happening?

Okay!

I would go up a size too. My son was leaking out of hist size 3 diapers a lot all of a sudden and I went up a size and it is all good agaib

He's 3 weeks tho! Does that matter at all or no?

No. I use them on my daughter and they don't leak. You probably need to go up a size like she said☝ @abeals04

Go up a size that's what I did my son was just to big for them