Offensive foul in post

[Num33BallerCCS]

Ok I'm a basketball player in High School here in California (CIF).

I used to play post a lot (i'm 6'4 and 168lbs), but due to my weight and how much i've progressed, I'm moving to a 2 or 3 guard. However, I'm sure there will be times when I will be matched up against smaller PFs or even centers.

I have a question for two rule sets: the NBA and high school in California.

If I am posting up my defender, can I "lower my shoulder" and do a power move to push him under the basket?

What if he is moving?

What if he has his feet set?

What if he is in the "no charge" circle under the basket?

Due do my weight, I need to dip my shoulder a little bit to put some force in the post or else I just get pushed out when I go to make a move.