When this occurs, immediately place your son in his crib or playpen and say, as you have been, "No biting." If you are consistent, even rigid, in this response, he will stop this. Remember not to take this personally. He has no capacity to empathize and he does not know about the impact of what he is doing.
Thank you so much for this service! I'm really beating myself up about this and hope you can give me some advice!