What to do when you stop getting paid off

[slugheads]

Before i start, i'd just like to say I'm a small stakes nl player.. However, since most of you probably have beaten ssnl before, as i have, i need to talk to you...

Heres the problem, i've always beaten ssnl but recently, im running into trouble... It seems my strategy just isn't getting paid off anymore, and the times I am getting paid off, im getting outdrawn...

I only play 2 pair or better postflop, and i play with relative idiots (people who will call with next to nothing)... THe problem is, these so called "idiots" aren't calling me down as much (and when the times they do call.. for example; I have AA, they call with 88 all i preflop) I lose the hand... OR, i have a set, they call all in with a flush on the turn, and hit it... Baffles the hell outta me how i am losing more money, than winning in these situations over the past 2 months...

SO, what should I do? THey fold when I bet, but when they call, and they are severely dominated (headsup) , they river me?

I basically, only play 2 pair or better postflop strongly... I bet, STRONGLY, always at least betting the pot when i know im ahead... Just getting rivered routinely on hands that should be winning...

And no, im not overvaluing TPTK, if anything, im undervaluing it.. But my goal in ssnl, is to double up, not win a small pot (that tptk usually wins)...