First of all, here's a hug for you!
This is a huge change. A huge, huge change, and it isn't going to happen all overnight. It's not going to be easy all the time, but it also isn't going to always be a huge struggle. One thing I have to ask about... What made you set a 3 pound per week goal? Realistically from what I understand, 2 pounds a week average is what's most sustainable... And even that isn't for everyone. I don't think it's very good to set yourself X number of pounds to lose per week, because so many different things effect your weight that can throw those plans off kilter, and then you'll be discouraged. For me, it works best to set myself mini goals. I might set a timeline for what would be nice... But I never expect it to work out just perfectly, because chances are it never will. I know you're aiming for a certain size for buying your wedding dress, but it's most important to approach your weight loss in a way that's sustainable for the long haul.
I'm not aiming to discourage you or anything like that, this is all just my two cents.
Good luck, and keep going! This is definitely doable.