It is July and so the grass is not the richest and assuming it is not overfeeding on creep and that you have wormed it, you might try 100 ml of live yogurt twice a day given by the drench gun. Continue for five days.
Before that however you might isolate the lambs on clean pasture and give a mixture of ivy leaves and willow leaves which seem to help dry it up. I might also give Spectam even though I usually give that at birth.
Clean and Fresh Water is really important to cleaning the digestive system out. I put out two gallon buckets and clean the bucket and refill twice per day in these cases.