The dryer tends to do that. I hang it out in the sun but I know you don’t get much sun in the UK, you can try adding a Napisan that is a whitening one that keeps whites bright. But I just hang them out we rarely use dryer. I have a lot of white clothes my fav is a white pair of skinny jeans lol
Napisan powder is great for baby related stains 😁 i try to soak them while they are fresh in the same as well
I use diluted bleach in water and soak whatever items need it for a few hours give it a good rinse out then put in the washing machine and they come out good as new
I soak whites in half a cup of Vanish Oxi White in a bucket of water, followed by a normal wash in the machine 😌
Put them out in the sun. It naturally bleaches them (even in the UK).
I put half a cup of baking soda in the washing machine.