Panda
Most people focus on a net weight loss/gain when evaluating progress. This method usually leads to failure in the long run due to the goal of hitting a number, like 150lbs. The better way to evaluate your progress is to measure the change in body fat composition. (I am assuming that you are trying to just lose fat and not alter your body structure.)
Most people have hit on the points you need to focus on to lose weight, resistance training, 5-6 smaller meals per day, limiting carbs to less-processed ones, and a net negative balance on caloric intake versus caloric burn. Dropping weight or adding (yes there are people who want to do this) weight is actually very simple when you have a plan and the discipline to stick to it. Most people lose the discipline when they do not see progress (weight lose in lbs).
If you are serious about this I would suggest having a hydrostatic body composition (I think this is the most accurate one. Calipers are very inaccurate and so is bio-impedance) test run to measure your baseline %, resting metabolic rate and most tests will also give you a report outlining your goal % and set the daily caloric levels you need along with the amount of calories you will burn during certain events. I would suggest doing test every 4-6 weeks depending how much of a control freak you are...I like 6 weeks.
As someone who has had to gain weight and then lose it as I have gotten older, I understand your frustration. There is no short cut and as someone touched on earlier this has to be a lifestyle change. You must be willing to maintain these lifestyle changes in order for you to keep your changed body structure.
A quick note on personal trainers...Most are completely uninformed, even the certified ones, and are a waste of your money. The signs of a good trainer are
Balances resistance training, cardio, flexibility and other activities tailored to your lifecycle (cycling, ply metrics, surfing, whatever) and adjusts the intensity as you progress
Creates a food plan with a sustainable approach for you
Gives equal weighting to the importance of health and appearance
Sets you up to reach your goal and maintain it without them...avoid the "drug dealer" trainers, the ones that convince you that you need to continue to use them to stay in shape
I am not in the training business, nor am I a workout freak, but I have had the chance to be trained by some of the best the NCAA has to offer and understand the method to the madness.
Good luck