Somethings happened to my dog, help!?

Well, my dog who is a Lab/Staff cross was playing in the garden, then she came in, hopping on 3 legs, crying in pain, so i carried her onto the sofa to see what's up. i checked if there are any thorns in her paw, but there's nothing. Her paw has also become flimsy and i have no idea what to do! Plus im home alone! Help, please?!