*sigh* Need some dieting help

I have been dieting since July. I joined the gym in September and go at least three times a week some times four. I got on the scale today and I've only lost 13 pounds in all that time. At one point I got down to losing 18 pounds, but somewhere in there I gained five pounds back again.

It's KILLING me. I just don't get it. I look at food and put on weight. I work so hard with little results. I can't really afford a personal trainer at the gym so I'm coming to you guys. I need to know what you've done to lose weight. Try a diet that worked really well? Know a lot about working out and have any pointers for me on what I should be doing? Only cardio for now? Weights too? I need all the help I can get. It's so frustrating to work so hard at something with such little results. To get to a point where I would be semi happy with myself before summer I need to lose 2.3 pounds a week. It won't be my final goal, but I figured setting short term goals would be good in the beginning. I know you're supposed to lose weight slow, but I don't think two pounds a week is too many to aim for.

So, give it too me! I need all the help I can get!