You can also call 111 any time and they can get you an out of hours gp appointment so you don’t have to wait until Monday x
If he has any other symptoms like fever, high temp, lethargic or dehydration, then take him in, otherwise I’d just keep cleaning and wait it out xx
My baby also has had a recurring gunky eye today , keep cleaning gently with warm sterile water and cotton pad and if still like it Monday go doctors x