"Usually within 15-20 minutes of tight play, I've doubled my money."

If you play tight for 15-20 minutes you should be playing roughly 4 hands.... think back, are you getting tptk or better on the first four hands you play consistently?

Do you mean that you're constantly being outgunned by straights/flushes/sets/full houses, or you're constantly being outgunned in the sense that you say have second pair, or tp good kick, and someone else has top pair or tptk or two pair and you call them down?

How often do you find yourself raising?

If i am heading down the wrong path, i don't mean to offend. If you really are just getting beaten bad, then i recommend playing more, and valuing TP less. most money isn't made off top pair, its made off better hands like sets or better. Top pair should be played fast, and generally wins small pots. If you have TPTK, and someone pushes at you, its safe to just fold it, because nobody else is going to be pushing without better.