My breastfed baby started waking up at 6months, 1 time per night, now at 1year& he wakes up 4 times per night. what should i do& what is the reason?

The reason is most..: ....Likely that he has come to understand that when he awakens and calls out, you come into the room. A 1 year old doesn't need to feed 4 times a night if he's eating well in daytime. Check to make sure he's ok (dry, not feverish etc.), then don't pick him up or otherwise indulge him. If he's physically ok, leave the room. Expect him to scream. He needs to learn to self soothe.