I have a rash with itching on the calves and in the upper area of the same I have what look like pimples. It has been extended, but more on one leg than on the other.
It is very difficult to determine exactly what may be unable to see the rash in person. But by your description it seems you may be experiencing some type of contact dermatitis allergic, by the fact that it is limited to a single leg. You should see your doctor to diagnose and treat it appropriately as it could be a fungus or other infection.