Am I doing something wrong?

[wellty08]

I play tight aggresive and after letting opponents suck out too many times I will now try to take the pot down after the flop or turn rather than trying to get in one more raise. However, lately my profits have gone down to nearly nothing. For example I will play for three to six hours and win only 15.00 and it only takes one bad beat (or read) to nullify my very slow and hard earned winnings. Last night I have pocket 77 and the flop comes 9 7 4 with two clubs and then the turn comes a meaningless 3 of spades so I raise the pot 3 times thinking I don't want anyone hitting their club flush draw. This guy raises and I think he has KK (or other big pair) and I got him with a set. We both go all in and he turns over pocket 56 wins with a double gapped str8!!!
Now all my profits are gone. I play for two more hours and don't lose anymore money but I didn't win either. How can I play for so many hours and not win anything? Am I too tight? should I play loose and bet more, but risk losing much more?
Any ideas out there?