Limping is a sign of pain and discomfort. The lameness can have various causes and therefore a physical examination is usually needed to make a correct assessment of the case.

A young growing dog with severe lameness or lameness due to trauma should be examined as soon as possible. This is because the lameness can be due to injuries or fractures in the growing zones (growth plates) of the bones and these require prompt treatment to prevent them from healing incorrectly. Keep the dog rested until examined by a vet, i.e. rest the dog on a lead and do not let it play with other dogs or run loose. Any form of jumping should also be strictly avoided.  

As discussed, I recommend that you contact your local vet or another available veterinarian for an emergency appointment as soon as possible.