breastfeeding question

So baby boy is three weeks old tomorrow. I had a great milk supply in both breasts until this week. Then out of no where my right breast stopped producing much milk. Like even when I pump I get less than an ounce of milk. LO prefers the left which is fine. I produce more than enough ( can feed and pump and still get 5 oz after nursing) just getting a little sore and somewhat concerned about my right breast. Anyone have this happen?