Try "yelping" loudly each time your puppy bites/chews on you. This mimics the way mom and littermates got the point across so they learn not to bite. Or say "no" loudly or "ouch". Something quick and loud to startle so they know they caused it. We use bitter apple too so there is also the "nasty taste" to reinforce the "yelp". Good luck, some "get it" sooner than others.
At 13 months old he should be learning that it's not "ok" to chew on your poor toes. After getting his attention with the "yelp" replace your toes with something extra special (and exceptable) to chew on. He'll get the point eventually. Always praise, praise, praise when he switches to the exceptable chew item.
Hang in there,