Great post Matt, and welcome Bianca,
I totally second what he said, as long as you have the fad diet mindset you will struggle! Find what your body needs and what it doesn't and change your lifestyle in a way that fits with your life! I still eat sweets, I still eat popcorn, I still eat stuff I like, and I have lost nearly 30 pounds... how come? Because I know how much I eat and I know what every food means.
I also blamed diseases (I am really asthmatic, and I suffer from coeliac disease, plus have thyroid problems) on my weigh gain but you know what, once I was properly medicated and stopped eating what hurt me (wheat in my case) it all boiled down to: if you eat more than you need, then you gain weight! Easy like that!
There are great posts on this board, the stickies will help you understand a lot, and the people here, they are awesome! Some have been on fad diets (such as south beach) and have worked them correctly, but most have found that if you feed your body the right stuff, your body will be happy and lose weight if you increase your activity level.
You don't need to do stuff you hate (I for instance don't like gyms that much, so I just swim mostly!), find what works for you, think about it, make a plan, if it doesn't work, discard it and make a new one with the lessons you learned from your first failed attempt!
I thought I could lose 40 pounds in 6 months but was wrong, I have been on it for 11 now and still have almost 12 to lose, but I have found that it is a bit trial and error and also you need to live while you lose weight. Sometimes living is mor important, and the weight loss comes second, sometimes your life is going great and you can put weightloss first. I have Minigoals (like your 20 pounds one) but I have often not met them. Oh well, it is good to have something that kicks your behind when you are not feeling up to it and every pound lost is a small triumph in itself.
Have a great weekend, Camy