some tables require a larger raise than others. 4x the big blind every time is a bad ammount for several reasons

-at some tables, 4x the big blind will get called by 3-5 players, not good
-at other tables, 4x will steal the blinds nearly every time, not good
-by raising the same ammount each time, players can put you on AA easier and get crazy implied odds for lots of speculative hands.

for instance, most live 1-2 and 2/4 games require at least a 5x the big blind raise to weed out players. yesterady at my casinos 1/2 game, 5x the big blind was a suitable ammount. usually got at least 1 caller. however ive been there where 10-15x the bb has been a neccesary raise to not get over 5 callers.

just feel out the table, and dont be afraid to mix it up. poker is a game of situations. every situation needs to be played accordingly. im not saying you are playing aces wrong, im just saying it would probably help to observe the type of preflop raises that seems to work at your table.

edit: oh yes, irexes reminded me, how is your postflop play?
eric lindgren said one of the smartest things ive ever heard. "an overpair to a flop is a good hand, but not a great hand"