I don't think you should have any discharge. Make sure he isn't licking the wound otherwise he could get it infected. I would call your vet as soon as possible, maybe they can give you a spray or salve to put on him to keep from infections. Also, you might want to get an e-collar to make sure he doesn't lick in the meantime.
The discharge does not sound good at all. I would call the vet for sure and keep him quiet as possible. This is just me, but, I always keep mine in their kennel and keep them from running or jumping and quiet as possible after any surgery. Hope he is okay.