I understand the prewedding big desire to LOSE some pounds. Everyone is watching the bride and we want to be beautiful on our big day. I'm sure you will be. I am guessing you realize that a super fast weight loss would not be long term. But you can do it for a wedding. :>) I get it. Not starving yourself is the hard part. You could greatly limit your food in the evening. Make your big meal breakfast or lunch and a small dinner and then skip eating after say 6:30 pm. When hungry, have a cup of tea. That helps. Drink a ton of water, full glass before a meal. And if you cut calories, remember, wedding day. :>) Those pictures are forever man. And then after you get back from your honeymoon, you can really think about lifestyle choices including diet and exercise to maintain a good weight for you. It's 70% what you eat. (or don't eat.). Good luck!!! And congrats on the big day!!
Losing weight permanently is a long-term process requiring a permanent change in how and what you eat and how you exercise. But 6 pounds in three weeks is doable if you don't care if you put the weight right back on again after your wedding, which you probably will if you don't make permanent changes. Just eat less and exercise more. But given the person you're marrying must like you the way you are, the slow way is the best because it will last.