I play 4NL, and find that quite frequently I am opening the pot with a 3x bet. The vast majority of the time it seems to be $0.12. I think about adding more bet sizes into my game, however, if it gets much high than $0.20, there seems to very rarely be any callers.

On hands like 99-JJ, 98s-KQs, and AJs-AQs, I'll open with a 4x bet.

On hands like QQ-AA and AK, I'll open with a 5x bet.

Since the vast majority of my hands I open with are 3x bets, am I giving away too much information about my hands? Should I have a wider range of bet sizes, and accept just the blinds as a payout when I hold very strong hands like QQ-AA and AK?

when i play nl i only vary my sizing preflop based on the number of limpers , not on my hand stength

Always raising larger with premium hands is definitely not advisable. Even a player who pays very little attention to their opponents should pick up on this tendency. Youv noted that your larger raises are generally illiciting folds so maybe some regs have already picked up this sizing tell.

Both previous posters nailed it. When you are varying opening sizes independent of position but solely based on hand strength it makes you easier to play against. If you open to 5x with your monster starting hands and opponents start catching on, you will not get any action from worse hands.

So, you want to be opening from 2.5-5BB (whatever you feel comfortable with but most people open 3x online) and then add 1BB to this raise size per limper.

So, if there's two limpers and your standard open size is 3BB, you would instead raise to 5BB and go from there. Always keep stack depth in mind though. If UTG limps with 12 BB and you pop it to 4 he is basically in shove/fold mode PF/on the flop.

Good luck!