Usually the obsessive licking is because their feet are itchy or they might have some kind of sore... I would think if it's causing a limp than there should be a sore...I would double-check the paws, vet might have missed something... In the mean time it can't hurt to keep those paws extra clean, in case of a wound (wouldn't want it to turn into an infection)...try the Epsom salts soak and dry those paws really well...keep us posted.