I hate my scale (the mystery of the 4 pound gain in 24 hours)

I hate my scale! Yes, I really do. Is it wrong to despise an inanimate object? Oh well, it’s true, it is my lifelong enemy. How can it be that I gained four pounds in one day? Yesterday I was feeling good about myself: I came to the false conclusion that I had lost 2 pounds, and I was in a positive mood. Today, my scale says (allegedly) that I have gained 2 pounds. (A four pound gain in only one day, from a loss to a gain of 2 pounds) How is this possible? Here was my day of eating yesterday: Breakfast: fiber one cereal, lunch: low fat cold cut sandwich, dinner: small lean hamburger with sautéed vegetables, and an apple. Does all of this manifest a four pound gain? I don’t think so. Now I feel confused and frustrated that I gained weight in the last month despite working out 4 times a week and eating a (mostly) healthy diet.
I don’t understand the art of weight loss. My body just does not want to give up the fat (my doctor even told me that). How many calories must I eat in a day, how many times must I work out in a week, in order to obtain my desired results? This is an ongoing struggle for me and I feel that I am losing it. No, seriously, I am losing it. Here are some possible factors: 1. I have a large bone structure, 2. I drink numerous glasses of water each day, 3. I take several different types of medication which could affect my weight. However, if these reasons do not change from day to day, then I cannot figure out this puzzle. I need some help: Any advice? I know that I always ask for comments but I really need some support, or just some tips, thank you all.
Dan