In NZ a product called scourban (pink chalky thick liquid that can be given direct or added to the milk) is available from vets, this is given a few times over a couple days and usually clears the scouring up very quickly. I think it is sulphur based and think that some vets dont suggest it anymore but mine does and it works - it may be similar to the kaolin?
There are also products that are better than straight electrolytes called i think diarrhrex (??) name may be wrong. These have worked better for me than straight electrolytes for scouring lambs and are ussually available for calves with the scours - there are plenty of medications available for scouring from vets and farm shops.
If there has been a long gap since you gave it milk, you will need to be very careful about giving it milk again as this will also upset its stomach and may cause more bloating- and here in NZ they say never change the milk type - as they are made from different products and can cause bloat if changed. As your lamb learns to eat grass, bloating can be a problem - there are lots of threads on bloating in lambs during weaning onto grass in this forum if you search it. Hay is good to calm the stomach and i agree with the others continue that with creep fed, lamb muesli in moderation till it is used to it and go carefully with the grass. Tend toward drier foods than scour making foods.
Others will know - i have forgotton but a lamb of five weeks probably if you are giving it hay, creep etc should be ok weaned from the milk - not ideal but better than scouring constantly. Generally i think with the electrolytes the container says give it for a limited period of time - is that right? Best check that or ask the vet. B12 injection may be useful - you will need to ask your vet.
If you do get it back on the milk safely, cooler milk with some yoghurt (add to each feed otherwise the whole bottle goes thick) will help prevent bloating and upset stomach.
I reckon like the others check with the vet re worms, cocc, etc. But likely just a sensitive stomach that over time will settle with some help re scourban or similar and the right feed. But it will be a daily managing thing until it settles
Is your lamb losing weight ? Have you talked more with the vet?
Sally in the north where are you??!She will have some ideas! Good luck.