Does he wriggle a lot. Our little one used to wriggle so much and pull his nappy down so now we take extra time to make sure the back is up as high as possible when changing. We also sized up to the nappies that range from like 8 - 19lbs which I think is size 3 in the Aldi ones Xx
This used to happen to my little boy, he’s also 3 months, someone told me that during the night the temperature drops and when they get a bit colder they tend to have fuller nappies meaning they leak more - I started making sure I change my LB before he’s about to sleep, i make sure the room is lovely & warm and I haven’t had an issue with leaking through since then,I also use fred&flo, little angels & pampers premium protection nappies, I hope this helps ☺️
I used to have this issue til I switched to rascals (rascals and friends) and I never have the issue now!!
I’ve used Fred and Flo (Tesco) Lidl and Aldi nappies and I’ve had no issues sounds weird but do you make sure his own is is pointing down? Leaks can happen if it’s not and that the slip bits are all the right way if that makes sense