Share '21 month son is this the norm?'

My son is 21 months and he has recently started saying mine to everything and telling everyone no. This is a new thing, I was wondering if I could get any better ideas for discipline. I do put him in timeout and I use a very direct apporoach to parenting. I am just stuck. He has also started screaming in me face when I tell him no. What do you do when this happens?