I can only guess based on the little information given, but my guess would be tha that you're getting punished by people calling you with speculative type hands. I suspect that they have you pegged as being so nitty that they know whether you've hit the flop before you do. They can call your bets with medium cards. When they don't see an Ace, King or Queen on the flop they can be pretty certain that you missed. When a big card hits the board they've probably got the fold button clicked before you've decided how much to bet. You're going to have to open up your range a bit. Obviously, I'm not going to define my range here, but it's tight enough that people learn not to call me light, but not so nitty that I don't get any action or become easily predictable.
I'm a believer in making standard sized raises so as not to give away the strength of my hand. I generally raise 3x + 1x for each limper in front of me with my whole range. My raises are generally the same size whether I'm holding Q-J or Q-Q, K-Q or A-A. If I wouldn't raise with it, then I usually wouldn't play it. At the same time, I don't find it necesssary to play every hand within my range. That is to say, the hands that I might raise with are not always the same hands that I would call a raise with, since I find that most players play a wider range than me, but have a tighter raising range than I do. Nor am I going to raise with hands at the bottom of my range from early position and maybe not from late position if there are too many players in the pot, and the raise size necessary to discourage them would be more than I would want to invest in those cards.