You've done just grand by the lamb. If the weather isn't too bad the mother and lamb will probably do better outside on the grass than inside felling couped up. The maggot oil is great stuf because not only does it sooth the skin but it also keeps the flys away. A good squirt of crovect will stop any reinfection. The stiff back legs is very likely due to the lamb feeling like its just slid dowm a tarmac road, bum first, at high apeed
Time, space and sunshine will do more good now than all the bottled preperations in the world!